NK/T-cell Lymphoma With Orbital Involvement: A Case Report and Systematic Review of the Literature

PURPOSE

To present the clinical course of a patient with recurrent NK/T-cell lymphoma (NKTL) involving the orbit and to review the literature on patients with NKTL involving the orbit.

METHODS

The PubMed database was searched for all cases of NKTL involving orbital, intraocular, or adnexal ocular structures.

RESULTS

Ninety-six patients were included in the final analysis. The mean age of diagnosis was 48.1 ± 16.8 years. The patients were 53/96 (55.2%) male and 43/96 (44.8%) female. Tumor location varied and included the orbit in 80/96 (83.3%), nasosinus in 56/96 (58.3%), uvea in 11/96 (11.5%), lacrimal gland in 9/96 (9.4%), lacrimal drainage system in 11/96 (11.5%), and conjunctiva in 7/96 (7.3%) cases. Management included surgical debulking in 29/96 (30.2%) cases, radiotherapy in 52/96 (54.2%) cases, and chemotherapy in 82/96 (85.4%) cases. Median survival was 6 months (95% CI: 5-9). Chemotherapy (hazard ratio = 0.80, 95% CI: 0.67-0.95, p = 0.013), radiotherapy (hazard ratio = 0.75, 95% CI: 0.64-0.87, p < 0.001), and orbital involvement being a recurrence of disease (hazard ratio = 0.79, 95% CI: 0.67-0.95, p = 0.009) were associated with improved survival. Advanced Ann Arbor stage (III-IV) at diagnosis (hazard ratio = 1.22, 95% CI: 1.08-1.38, p = 0.001), vision loss (hazard ratio = 1.18, 95% CI: 1.04-1.34, p = 0.009), proptosis (hazard ratio = 1.15, 95% CI: 1.01-1.30, p = 0.035) and periorbital swelling (hazard ratio = 1.15, 95% CI: 1.00-1.33, p = 0.048) were associated with poor survival.

CONCLUSIONS

NK/T-cell lymphoma involving the orbit, globe, or ocular adnexa heralds a poor prognosis where early diagnosis and therapy are critical. The use of radiotherapy and chemotherapy is associated with improved survival.

Chronic Lymphocytic Leukemia Presenting as Bilateral Periorbital Edema Treated With Low-dose Radiation Therapy

Ocular manifestations in chronic lymphocytic leukemia (CLL) have been reported in 30% to 40% of patients and may be a result of direct tissue infiltration, concomitant blood dyscrasias, or a result of therapeutic intervention. Leukemia cutis, defined as infiltration of the epidermis or dermis by neoplastic lymphocytes, is rare. Herein, we present a case report of a patient with leukemia who presented with periorbital edema and ecchymosis. This is the first known case to date of periorbital CLL successfully treated with low-dose radiation therapy (4 Gy in 2 fractions). Clinicians should be aware of the possibility of ocular involvement from CLL, given the importance of prompt diagnosis and treatment.

Computational pathology in 2030: a Delphi study forecasting the role of AI in pathology within the next decade

BACKGROUND

Artificial intelligence (AI) is rapidly fuelling a fundamental transformation in the practice of pathology. However, clinical integration remains challenging, with no AI algorithms to date in routine adoption within typical anatomic pathology (AP) laboratories. This survey gathered current expert perspectives and expectations regarding the role of AI in AP from those with first-hand computational pathology and AI experience.

METHODS

Perspectives were solicited using the Delphi method from 24 subject matter experts between December 2020 and February 2021 regarding the anticipated role of AI in pathology by the year 2030. The study consisted of three consecutive rounds: 1) an open-ended, free response questionnaire generating a list of survey items; 2) a Likert-scale survey scored by experts and analysed for consensus; and 3) a repeat survey of items not reaching consensus to obtain further expert consensus.

FINDINGS

Consensus opinions were reached on 141 of 180 survey items (78.3%). Experts agreed that AI would be routinely and impactfully used within AP laboratory and pathologist clinical workflows by 2030. High consensus was reached on 100 items across nine categories encompassing the impact of AI on (1) pathology key performance indicators (KPIs) and (2) the pathology workforce and specific tasks performed by (3) pathologists and (4) AP lab technicians, as well as (5) specific AI applications and their likelihood of routine use by 2030, (6) AI's role in integrated diagnostics, (7) pathology tasks likely to be fully automated using AI, and (8) regulatory/legal and (9) ethical aspects of AI integration in pathology.

INTERPRETATION

This systematic consensus study details the expected short-to-mid-term impact of AI on pathology practice. These findings provide timely and relevant information regarding future care delivery in pathology and raise key practical, ethical, and legal challenges that must be addressed prior to AI's successful clinical implementation.

FUNDING

No specific funding was provided for this study.

Local recurrence of uveal melanoma and concomitant brain metastases associated with an activating telomerase promoter mutation seven years after secondary enucleation

Purpose

To describe a case of local recurrence of uveal melanoma with concomitant brain metastases after secondary enucleation.

Observations

A 73 year-old patient presented with dizziness and gait instability. MRI of the orbits and brain showed an anophthalmic socket with an orbital implant and an associated optic nerve mass as well as multiple mass lesions in the brain. The patient's history was significant for secondary enucleation for uveal melanoma recurrence seven years prior to presentation. Histopathology of the enucleated eye revealed no signs of extrascleral extension or optic nerve invasion. Biopsy of the optic nerve mass confirmed recurrent uveal melanoma with somatic mutations in GNAQ (Q209L) and the telomerase (TERT) promoter (c.1-124C > T) found on targeted next-generation sequencing (NGS). The same mutations were found in the primary tumor in the patient's archived enucleation samples.

Conclusions

Local recurrence of uveal melanoma can occur after enucleation and is associated with an increased risk of systemic metastases. It is important for clinicians to monitor patients for local recurrence and systemic metastases even after enucleation. Genetic biomarkers may play an important role in identifying tumors at highest risk of local recurrence and metastasis. To our knowledge, this is the first case study to describe the TERT promoter mutation c.1-124C > T in the setting of recurrent uveal melanoma.

Primary Mesenchymal Tumors of the Thyroid Gland: A Modern Retrospective Cohort Including the First Case of TFE3-Translocated Malignant Perivascular Epithelioid Cell Tumor (PEComa)

Primary mesenchymal tumors of the thyroid gland are extremely rare, with only case reports and small case series documented in the English literature, many of which were published prior to the era of molecular pathology. In the current study, we aim to present a contemporary multi-centric cohort of thyroid mesenchymal tumors. Nineteen primary thyroid mesenchymal tumors were collected from three tertiary centers. Their clinicopathologic features, immunoprofile, molecular alterations, and outcome were described. Eight cases were classified as benign or intermediate with solitary fibrous tumor being the most common histotype (n = 3). The remaining 11 cases were malignant, including three angiosarcomas, one epithelioid hemangioendothelioma, one adamantinoma-like Ewing sarcoma, one biphasic synovial sarcoma, one malignant melanocytic peripheral nerve sheath tumor (melanotic schwannoma), one myxofibrosarcoma, and two undifferentiated pleomorphic/spindle sarcomas (one of which was radiation-induced). Six tumors showed characteristic diagnostic translocations. We herein also described the first case of thyroid malignant perivascular epithelioid cell tumor (PEComa) with RBM10-TFE3 fusion in a 35-year-old female patient. Thyroid mesenchymal tumors, benign or malignant, are rare with a broad spectrum of possible diagnoses. A comprehensive examination to include histology, immunohistochemistry, and molecular testing is essential for the correct diagnosis and to distinguish them from anaplastic thyroid carcinoma. PEComa may occur as a primary tumor of the thyroid gland, expanding the histologic spectrum of thyroid mesenchymal tumors.

Cilioretinal Artery Occlusion as the Presenting Manifestation of Left Atrial Myxoma

Purpose:

This work reports a case of left atrial myxoma presenting with cilioretinal artery occlusion.

Methods:

A case report is discussed.

Results:

A 57-year-old man was referred for acute vision loss in the left eye after a workup including electrocardiogram, magnetic resonance imaging of the brain without contrast, computed tomography angiography of the head and neck, erythrocyte sedimentation rate, and C-reactive protein had negative results. Examination revealed cilioretinal artery occlusion with visible emboli. Because an echocardiogram was not performed, the patient was referred to the emergency department. Echocardiogram revealed a large left atrial mass prolapsing into the left ventricle. The mass was excised, and pathology showed myxoma.

Conclusions:

This is the first case to our knowledge of isolated cilioretinal artery occlusion as the initial presentation of an atrial myxoma. Thorough and complete workup was crucial to averting further morbidity and mortality.

An Analysis of the Effect of the COVID-19 Pandemic on Case Volumes in an Academic Subspecialty-Based Anatomic Pathology Practice

The recent COVID pandemic has had a major effect on anatomic pathology specimen volumes across the country. The effect of this pandemic on a subspecialty academic practice is presented. We used a data-driven approach to monitor the changing workloads in a granular fashion and dynamically adjust the scheduling of faculty and histology staff accordingly to minimize the number of people present on-site. At the peak of the pandemic locally, the main hospital in our health system had 450 COVID-positive inpatients. The surgical pathology specimen volume dropped to 13% of the pre-pandemic levels, and this occurred about 2 weeks before the peak of the inpatient census; cytology specimens (the majority of which are outreach gynecological) dropped to approximately 5% of the pre-pandemic volume, 4 weeks before the peak inpatient census. All of the surgical subspecialty services showed a significant decrease in volume, with hematopathology being the least affected (dropped to 30% of the pre-pandemic level). The genitourinary surgical subspecialty service (predominantly prostate and bladder biopsies) was the most affected (dropped to 1% of the pre-pandemic level) but was fastest to return as clinical operations began to return to normal. The only specimen type which showed a significant increase in turnaround time during the pandemic was our gynecologic cytology specimens and that occurred as the specimen volume returned. This was due to stay-at-home directives for the cytotechnologists and the fact that some of them were retasked to participate in our SARS-CoV-2 testing.

A Semiquantitative Scoring System May Allow Biopsy Diagnosis of Pulmonary Large Cell Neuroendocrine Carcinoma

OBJECTIVES

The aim of this study was to devise reproducible biopsy criteria for distinguishing pulmonary large cell neuroendocrine carcinoma (LCNEC) from non-small cell lung carcinoma (NSCLC).

METHODS

Tissue microarrays of LCNEC and NSCLC were generated from resection specimens and used as biopsy surrogates. They were stained for neuroendocrine markers, Ki-67, napsin-A, and p40, and independently analyzed by standardized morphologic criteria by four pathologists. Tumors were scored based on morphology, neuroendocrine marker expression, and Ki-67 proliferative index.

RESULTS

The average total score for LCNEC was significantly higher than for NSCLC (5.65 vs 0.51, P < .0001). Utilizing a cutoff score of 4 or higher showed 100% sensitivity and 99% specificity for LCNEC diagnosis, with an excellent agreement among four pathologists (98%).

CONCLUSIONS

The proposed semiquantitative approach based on a combination of specific morphologic and immunophenotypic features may be a useful tool for biopsy diagnosis of LCNEC.

A Survey of LOINC Code Selection Practices Among Participants of the College of American Pathologists Coagulation (CGL) and Cardiac Markers (CRT) Proficiency Testing Programs

Context.—

Biomedical terminologies such as Logical Observation Identifiers, Names, and Codes (LOINC) were developed to enable interoperability of health care data between disparate health information systems to improve patient outcomes, public health, and research activities.

Objective.—

To ascertain the utilization rate and accuracy of LOINC terminology mapping to 10 commonly ordered tests by participants of the College of American Pathologists (CAP) Proficiency Testing program.

Design.—

Questionnaires were sent to 1916 US and Canadian laboratories participating in the 2018 CAP coagulation (CGL) and/or cardiac markers (CRT) surveys requesting information on practice setting, instrument(s) and test method(s), and LOINC code selection and usage in the laboratory and electronic health records.

Results.—

Ninety of 1916 CGL and/or CRT participants (4.7%) responded to the questionnaire. Of the 275 LOINC codes reported, 54 (19.6%) were incorrect: 2 codes (5934-2 and 12345-1) (0.7%) did not exist in the LOINC database and the highest error rates were observed in the property (27 of 275, 9.8%), system (27 of 275, 9.8%), and component (22 of 275, 8.0%) LOINC axes. Errors in LOINC code selection included selection of the incorrect component (eg, activated clotting time instead of activated partial thromboplastin time); selection of panels that can never be used to obtain an individual analyte (eg, prothrombin time panel instead of international normalized ratio); and selection of an incorrect specimen type.

Conclusions.—

These findings of real-world LOINC code implementation across a spectrum of laboratory settings should raise concern about the reliability and utility of using LOINC for clinical research or to aggregate data.

Dabrafenib and Trametinib for BRAF-Mutated Conjunctival Melanoma

Background

Conjunctival melanoma is a potentially lethal malignancy of the ocular surface. There have been no therapeutic advancements made in the past several decades despite increasing prevalence of the disease.

Methods

The authors report the case of a 52-year-old Caucasian male with unresectable, recurrent conjunctival melanoma with V600 BRAF mutation who was treated with systemic BRAF/MEK inhibition.

Results

There was complete regression of local disease within the first 9 months. The patient remains without local recurrence or systemic metastasis at 1 year.

Conclusion

This is the first reported case of conjunctival melanoma with complete response to BRAF/MEK inhibition. As long as targeted therapy remains an option, patients with conjunctival melanoma should undergo mutational profiling of their tumor.

Immune Checkpoint Inhibitor-Associated Pericarditis

Side effects of immune checkpoint inhibitors, termed immune-related adverse events, are relatively common, but immune checkpoint inhibitor-mediated cardiotoxicities are rare; however, they can be serious and potentially fatal. Pericarditis is an infrequent cardiac toxicity of immunotherapy and predisposing factors remain unknown. Here we report three patients with NSCLC who developed pericarditis during therapy with programmed death 1/programmed death ligand 1+/- CTLA-4 inhibitors. We review the clinical presentation of these three cases and histopathologic findings from autopsies from the first two patients and a pericardial sampling that has been obtained from a pericardial window procedure in the third patient who recovered from the pericarditis episode. We also discuss the potential mechanisms, as well as what is known about pericarditis secondary to immune-related adverse events.

Acute Presentation of Mesectodermal Leiomyoma of the Ciliary Body

Purpose

We report a case of acutely presenting mesectodermal leiomyoma of the ciliary body in a 29-year-old female who reported waking up with swollen eyelids of the right eye and light-perception vision. The affected eye had elevated intraocular pressure, a flat anterior chamber, and a pale, round mass arising from the nasal ciliary body, invading the angle and protruding into the visual axis posterior to the lens. Within days, the visual acuity decreased to no light perception. The eye was enucleated.

Methods

The enucleated eye harbored a tumor arising from the ciliary body, measuring 18 mm in the greatest dimension. Spindled cells with fibrillary cytoplasmic processes suggested a neural origin though negative for S-100, Melan-A, and HMB-45. The cells stained strongly positive for smooth muscle actin and vimentin, leading to the diagnosis of mesectodermal leiomyoma of the ciliary body.

Results

We review the literature to expand upon the clinical findings, diagnostic methods, and histopathologic and immunohistochemistry characteristics of mesectodermal leiomyoma.

Conclusion

Leiomyoma must be in the differential diagnosis for ciliary body mass, especially in women of reproductive age. Diagnosis relies on histopathology and immunohistochemistry. The mechanism of acute symptom onset may be multifactorial. This case emphasizes the possibility of acute presentation of a rare, benign intraocular tumor.

Pathology Informatics Essentials for Residents: A Flexible Informatics Curriculum Linked to Accreditation Council for Graduate Medical Education Milestones (a secondary publication)

CONTEXT

Recognition of the importance of informatics to the practice of pathology has surged. Training residents in pathology informatics has been a daunting task for most residency programs in the United States because faculty often lacks experience and training resources. Nevertheless, developing resident competence in informatics is essential for the future of pathology as a specialty.

OBJECTIVE

To develop and deliver a pathology informatics curriculum and instructional framework that guides pathology residency programs in training residents in critical pathology informatics knowledge and skills, and meets Accreditation Council for Graduate Medical Education Informatics Milestones.

DESIGN

The College of American Pathologists, Association of Pathology Chairs, and Association for Pathology Informatics formed a partnership and expert work group to identify critical pathology informatics training outcomes and to create a highly adaptable curriculum and instructional approach, supported by a multiyear change management strategy.

RESULTS

Pathology Informatics Essentials for Residents (PIER) is a rigorous approach for educating all pathology residents in important pathology informatics knowledge and skills. PIER includes an instructional resource guide and toolkit for incorporating informatics training into residency programs that vary in needs, size, settings, and resources. PIER is available at http://www.apcprods.org/PIER (accessed April 6, 2016).

CONCLUSIONS

PIER is an important contribution to informatics training in pathology residency programs. PIER introduces pathology trainees to broadly useful informatics concepts and tools that are relevant to practice. PIER provides residency program directors with a means to implement a standardized informatics training curriculum, to adapt the approach to local program needs, and to evaluate resident performance and progress over time.

Pathology Informatics Essentials for Residents: A Flexible Informatics Curriculum Linked to Accreditation Council for Graduate Medical Education Milestones

CONTEXT

-Recognition of the importance of informatics to the practice of pathology has surged. Training residents in pathology informatics has been a daunting task for most residency programs in the United States because faculty often lacks experience and training resources. Nevertheless, developing resident competence in informatics is essential for the future of pathology as a specialty.

OBJECTIVE

-To develop and deliver a pathology informatics curriculum and instructional framework that guides pathology residency programs in training residents in critical pathology informatics knowledge and skills, and meets Accreditation Council for Graduate Medical Education Informatics Milestones.

DESIGN

-The College of American Pathologists, Association of Pathology Chairs, and Association for Pathology Informatics formed a partnership and expert work group to identify critical pathology informatics training outcomes and to create a highly adaptable curriculum and instructional approach, supported by a multiyear change management strategy.

RESULTS

-Pathology Informatics Essentials for Residents (PIER) is a rigorous approach for educating all pathology residents in important pathology informatics knowledge and skills. PIER includes an instructional resource guide and toolkit for incorporating informatics training into residency programs that vary in needs, size, settings, and resources. PIER is available at http://www.apcprods.org/PIER (accessed April 6, 2016).

CONCLUSIONS

-PIER is an important contribution to informatics training in pathology residency programs. PIER introduces pathology trainees to broadly useful informatics concepts and tools that are relevant to practice. PIER provides residency program directors with a means to implement a standardized informatics training curriculum, to adapt the approach to local program needs, and to evaluate resident performance and progress over time.

Pathology Informatics Essentials for Residents: A flexible informatics curriculum linked to Accreditation Council for Graduate Medical Education milestones

Context:

Recognition of the importance of informatics to the practice of pathology has surged. Training residents in pathology informatics have been a daunting task for most residency programs in the United States because faculty often lacks experience and training resources. Nevertheless, developing resident competence in informatics is essential for the future of pathology as a specialty.

Objective:

The objective of the study is to develop and deliver a pathology informatics curriculum and instructional framework that guides pathology residency programs in training residents in critical pathology informatics knowledge and skills and meets Accreditation Council for Graduate Medical Education Informatics Milestones.

Design:

The College of American Pathologists, Association of Pathology Chairs, and Association for Pathology Informatics formed a partnership and expert work group to identify critical pathology informatics training outcomes and to create a highly adaptable curriculum and instructional approach, supported by a multiyear change management strategy.

Results:

Pathology Informatics Essentials for Residents (PIER) is a rigorous approach for educating all pathology residents in important pathology informatics knowledge and skills. PIER includes an instructional resource guide and toolkit for incorporating informatics training into residency programs that vary in needs, size, settings, and resources. PIER is available at http://www.apcprods.org/PIER (accessed April 6, 2016).

Conclusions:

PIER is an important contribution to informatics training in pathology residency programs. PIER introduces pathology trainees to broadly useful informatics concepts and tools that are relevant to practice. PIER provides residency program directors with a means to implement a standardized informatics training curriculum, to adapt the approach to local program needs, and to evaluate resident performance and progress over time.

Computational Pathology: A Path Ahead

CONTEXT

We define the scope and needs within the new discipline of computational pathology, a discipline critical to the future of both the practice of pathology and, more broadly, medical practice in general.

OBJECTIVE

To define the scope and needs of computational pathology.

DATA SOURCES

A meeting was convened in Boston, Massachusetts, in July 2014 prior to the annual Association of Pathology Chairs meeting, and it was attended by a variety of pathologists, including individuals highly invested in pathology informatics as well as chairs of pathology departments.

CONCLUSIONS

The meeting made recommendations to promote computational pathology, including clearly defining the field and articulating its value propositions; asserting that the value propositions for health care systems must include means to incorporate robust computational approaches to implement data-driven methods that aid in guiding individual and population health care; leveraging computational pathology as a center for data interpretation in modern health care systems; stating that realizing the value proposition will require working with institutional administrations, other departments, and pathology colleagues; declaring that a robust pipeline should be fostered that trains and develops future computational pathologists, for those with both pathology and nonpathology backgrounds; and deciding that computational pathology should serve as a hub for data-related research in health care systems. The dissemination of these recommendations to pathology and bioinformatics departments should help facilitate the development of computational pathology.

Accreditation and regulatory implications of electronic health records for laboratory reporting

The Clinical Laboratory Improvement Amendments of 1988 include strict regulations for reporting content, and it falls on the named director to ensure that this content is available to the caregiver. With the electronic health record serving as the conduit to the end user of the laboratory data, the laboratory generally, and the director specifically, must verify accurate transmission of these content components. An understanding of regulatory and accreditation requirements is essential both to allow the proper discharge of these mandated responsibilities and to enforce the role and authority that the pathologist must have to ensure that these requirements are satisfied by the reporting system. The regulatory requirements will be discussed in the context of the Clinical Laboratory Improvement Amendments of 1988 standards; however, interpretation and expansion on these regulations exist both in Clinical Laboratory Improvement Amendments of 1988 inspection guidelines from the Centers for Medicare and Medicaid Services and in accreditation program requirements. This regulatory expectation both places the laboratory director in a position of risk and provides leverage to ensure meaningful and accurate communication of laboratory information.

Stand-alone laboratory information systems versus laboratory modules incorporated in the electronic health record

The increasing availability of laboratory information management modules within enterprise electronic health record solutions has resulted in some institutional administrators deciding which laboratory information system will be used to manage workflow within the laboratory, often with minimal input from the pathologists. This article aims to educate pathologists on many of the issues and implications this change may have on laboratory operations, positioning them to better evaluate and represent the needs of the laboratory during this decision-making process. The experiences of the authors, many of their colleagues, and published observations relevant to this debate are summarized. There are multiple dimensions of the interdependency between the pathology laboratory and its information system that must be factored into the decision. Functionality is important, but management authority and gap-ownership are also significant elements to consider. Thus, the pathologist must maintain an active role in the decision-making process to ensure the success of the laboratory.

Management of laboratory data and information exchange in the electronic health record

In the era of the electronic health record, the success of laboratories and pathologists will depend on effective presentation and management of laboratory information, including test orders and results, and effective exchange of data between the laboratory information system and the electronic health record. In this third paper of a series that explores empowerment of pathology in the era of the electronic health record, we review key elements of managing laboratory information within the electronic health record and examine functional issues pertinent to pathologists and laboratories in the exchange of laboratory information between electronic health records and both anatomic and clinical pathology laboratory information systems. Issues with electronic order-entry and results-reporting interfaces are described, and considerations for setting up these interfaces are detailed in tables. The role of the laboratory medical director as mandated by the Clinical Laboratory Improvement Amendments of 1988 and the impacts of discordance between laboratory results and their display in the electronic health record are also discussed.

Pathologists as Stewards of Laboratory Information

Just as electronic health records are transforming the practice of medicine and health care information management, practicing in the era of the electronic health record offers opportunities, if not imperatives, for pathologists to take on new and “transformative” professional and leadership roles for the organizations they serve. Experience indicates that clinicians will perceive pathologists and laboratories as responsible for all aspects of laboratory testing and information management, including order entry and results reporting, even though such functions may fall beyond the control of the laboratory. As described and expanded upon in the previous 4 articles of this series, the use of electronic health records dictates changes in how clinicians interact with laboratory information. In this environment, pathologists are uniquely positioned to act as the stewards for laboratory information in electronic health records and throughout health care organizations.

Pathologists' place in the electronic health record landscape

With growth spurred by recent federal efforts, electronic health records (EHRs) are transforming the practice of medicine and have important implications for pathologists, their laboratories, and the patients they serve. Beyond new EHR-related regulatory requirements, EHRs fundamentally alter the way clinicians interact with laboratory information, including test order entry and result reviewing. This article is the first in a series of 5 related articles whose goal is to provide a "framework" for empowering pathologists to adapt to, and to succeed in, the era of expanding EHR use. This series aims to describe the environment for EHR uptake, to raise awareness of EHR-related issues that pathologists and laboratories face, and to explore new professional roles for pathologists as stewards of patients' laboratory information in EHRs.

Pathology training in informatics: evolving to meet a growing need

CONTEXT

The mechanics of the practice of medicine in general and of pathology in particular is evolving rapidly with the rise in the use of electronic information systems for managing the care of individual patients, including the ordering and reporting of laboratory tests, maintaining the health of served populations, and documenting the full range of health care activities. Pathologists currently in practice and those in training need to acquire additional skills in informatics to be prepared to maintain a central role in patient care.

OBJECTIVE

To summarize the evolving landscape of pathology informatics, with particular attention to the preparation of pathologists for this discipline and to the possible influence of the new subspecialty certification in clinical informatics.

DATA SOURCES

Most of the information discussed is drawn from the authors' direct experience with informatics, resident and fellow education, and the organizations supporting these activities in pathology.

CONCLUSIONS

The increasing reliance of medical practice on electronic health records and other clinical information systems is creating a greater need for physicians skilled in the use and management of these tools. The establishment of clinical informatics as a formal subspecialty in medicine will likely help secure a role for physicians within information management structures at health care institutions. Pathologists must actively engage in informatics to assure that our specialty is appropriately recognized and represented in this growing discipline.

Validating whole slide imaging for diagnostic purposes in pathology: guideline from the College of American Pathologists Pathology and Laboratory Quality Center

CONTEXT

There is increasing interest in using whole slide imaging (WSI) for diagnostic purposes (primary and/or consultation). An important consideration is whether WSI can safely replace conventional light microscopy as the method by which pathologists review histologic sections, cytology slides, and/or hematology slides to render diagnoses. Validation of WSI is crucial to ensure that diagnostic performance based on digitized slides is at least equivalent to that of glass slides and light microscopy. Currently, there are no standard guidelines regarding validation of WSI for diagnostic use.

OBJECTIVE

To recommend validation requirements for WSI systems to be used for diagnostic purposes.

DESIGN

The College of American Pathologists Pathology and Laboratory Quality Center convened a nonvendor panel from North America with expertise in digital pathology to develop these validation recommendations. A literature review was performed in which 767 international publications that met search term requirements were identified. Studies outside the scope of this effort and those related solely to technical elements, education, and image analysis were excluded. A total of 27 publications were graded and underwent data extraction for evidence evaluation. Recommendations were derived from the strength of evidence determined from 23 of these published studies, open comment feedback, and expert panel consensus.

RESULTS

Twelve guideline statements were established to help pathology laboratories validate their own WSI systems intended for clinical use. Validation of the entire WSI system, involving pathologists trained to use the system, should be performed in a manner that emulates the laboratory's actual clinical environment. It is recommended that such a validation study include at least 60 routine cases per application, comparing intraobserver diagnostic concordance between digitized and glass slides viewed at least 2 weeks apart. It is important that the validation process confirm that all material present on a glass slide to be scanned is included in the digital image.

CONCLUSIONS

Validation should demonstrate that the WSI system under review produces acceptable digital slides for diagnostic interpretation. The intention of validating WSI systems is to permit the clinical use of this technology in a manner that does not compromise patient care.

In vitro and in vivo comparison of two suprachoroidal shunts

PURPOSE

To compare fibrosis, aqueous humor dynamics, and intraocular pressure (IOP) of two suprachoroidal shunts as part of a new class of glaucoma drainage devices.

METHODS

Following proliferation analysis in vitro, 20 rabbits were implanted with either a gold shunt (GS, GMSplus+, SOLX) or a polypropylene shunt (PS, Aquashunt, OPKO). Ten eyes received mitomycin C (MMC) and triamcinolone. Peak and trough IOP were monitored with a pneumatonometer and tono-pen for 15 weeks. Aqueous humor dynamics were evaluated fluorophotometrically and tonographically. Fibrosis was quantified.

RESULTS

In vitro proliferation was similar. In vivo, both shunts were devoid of foreign body reaction but exhibited fibrosis, and GS showed vascularization. There was no significant difference in aqueous or uveoscleral flow. Preoperative morning IOP was 23.7 ± 2 mm Hg, and evening IOP was 26.5 ± 2 mm Hg (P = 0.000). Morning IOP was decreased through 15 weeks and evening IOP through 8 weeks in all groups. The morning IOP decrease was most profound at 15 weeks in PS (41%) compared to GS (18%). Antifibrotics initially enhanced but eventually diminished shunt performance. At 15 weeks, thickness of scleral fibrosis was greater in GS (246 ± 47 μm) and PS (188 ± 47 μm, P = 0.285) compared with GS+MMC (109 ± 26 μm, P = 0.023 to GS) and PS+MMC (48 ± 30 μm, P = 0.028 to PS).

CONCLUSIONS

In a rabbit model, suprachoroidal polypropylene and gold shunts allow access to a new drainage pathway with different IOP profiles that can be modified with antifibrotics.

Tracking in Anatomic Pathology

Bar code–based tracking solutions, long present in clinical pathology laboratories, have recently made an appearance in anatomic pathology (AP) laboratories. Tracking of AP “assets” (specimens, blocks, slides) can enhance laboratory efficiency, promote patient safety, and improve patient care. Routing of excess clinical material into research laboratories and biorepositories are other avenues that can benefit from tracking of AP assets. Implementing tracking is not as simple as installing software and turning it on. Not all tracking solutions are alike. Careful analysis of laboratory workflow is needed before implementing tracking to assure that this solution will meet the needs of the laboratory. Such analysis will likely uncover practices that may need to be modified before a tracking system can be deployed. Costs that go beyond simply that of purchasing software will be incurred and need to be considered in the budgeting process. Finally, people, not technology, are the key to assuring quality. Tracking will require significant changes in workflow and an overall change in the culture of the laboratory. Preparation, training, buy-in, and accountability of the people involved are crucial to the success of this process. This article reviews the benefits, available technology, underlying principles, and implementation of tracking solutions for the AP and research laboratory.

Accounting for the professional work of pathologists performing autopsies

CONTEXT

With an increasing trend toward fee-code-based methods of measuring the clinical professional productivity of pathologists, those pathologists whose clinical activities include the performance of autopsies have been disadvantaged by the lack of generally accepted workload equivalents for autopsy performance and supervision.

OBJECTIVE

To develop recommended benchmarks to account for this important and often overlooked professional activity.

DESIGN

Based on the professional experience of members of the Autopsy Committee of the College of American Pathologists, a survey of autopsy pathologists, and the limited additional material available in the literature, we developed recommended workload equivalents for the professional work associated with performing an autopsy, which we elected to express as multiples of established Current Procedural Terminology codes.

RESULTS

As represented in Table 3 , we recommend that the professional work associated with a full adult autopsy be equivalent to 5.5 × 88309-26. Additional professional credit of 1.5 × 88309-26 should be added for evaluation of the brain and for a detailed clinical-pathologic discussion. The corresponding value for a fetal/neonatal autopsy is 4.0 × 88309-26.

CONCLUSION

Although we recognize that autopsy practices vary significantly from institution to institution, it is hoped that our proposed guidelines will be a valuable starting point that individual practices can then adapt, taking into account the specifics of their practice environment.

Custom software development for use in a clinical laboratory

In-house software development for use in a clinical laboratory is a controversial issue. Many of the objections raised are based on outdated software development practices, an exaggeration of the risks involved, and an underestimation of the benefits that can be realized. Buy versus build analyses typically do not consider total costs of ownership, and unfortunately decisions are often made by people who are not directly affected by the workflow obstacles or benefits that result from those decisions. We have been developing custom software for clinical use for over a decade, and this article presents our perspective on this practice. A complete analysis of the decision to develop or purchase must ultimately examine how the end result will mesh with the departmental workflow, and custom-developed solutions typically can have the greater positive impact on efficiency and productivity, substantially altering the decision balance sheet. Involving the end-users in preparation of the functional specifications is crucial to the success of the process. A large development team is not needed, and even a single programmer can develop significant solutions. Many of the risks associated with custom development can be mitigated by a well-structured development process, use of open-source tools, and embracing an agile development philosophy. In-house solutions have the significant advantage of being adaptable to changing departmental needs, contributing to efficient and higher quality patient care.

Pathology informatics fellowship retreats: The use of interactive scenarios and case studies as pathology informatics teaching tools

Background:

Last year, our pathology informatics fellowship added informatics-based interactive case studies to its existing educational platform of operational and research rotations, clinical conferences, a common core curriculum with an accompanying didactic course, and national meetings.

Methods:

The structure of the informatics case studies was based on the traditional business school case study format. Three different formats were used, varying in length from short, 15-minute scenarios to more formal multiple hour-long case studies. Case studies were presented over the course of three retreats (Fall 2011, Winter 2012, and Spring 2012) and involved both local and visiting faculty and fellows.

Results:

Both faculty and fellows found the case studies and the retreats educational, valuable, and enjoyable. From this positive feedback, we plan to incorporate the retreats in future academic years as an educational component of our fellowship program.

Conclusions:

Interactive case studies appear to be valuable in teaching several aspects of pathology informatics that are difficult to teach in more traditional venues (rotations and didactic class sessions). Case studies have become an important component of our fellowship's educational platform.

Overcoming the Limitations of Integrated Clinical Digital Imaging Solutions

Context.—Digital imaging is increasingly common in medicine. Vendors of anatomic pathology software have addressed this need by integrating digital image acquisition and storage into their products. While offering a number of advantages, these solutions cannot be easily adapted to accommodate the existing work flow for many pathology departments.

Objective.—To describe a novel solution that maintains the advantages of these integrated solutions but offers many additional flexibilities, making it more compatible with the work flow in most clinical departments.

Design.—This solution involves separating the image acquisition step from the image archiving process and creating dual-image storages for greater usability. Software needed to deploy this modular and scalable solution is described.

Results.—We have deployed this solution at our institution and achieved widespread acceptance and use, with minimal training required. Deployment in the surgical pathology gross specimen room, in particular, has resulted in a significant increase in the number of photographs taken and the percentage of cases documented photographically.

Conclusions.—The complete clinical digital imaging solution described herein is an effective, scalable solution for pathology imaging at a departmental level. Although developed and implemented in an anatomic pathology department, the method described is generally applicable to digital imaging in any large multiuser environment.

Glandular patterns in a thyroid carcinoma with insular and anaplastic features: a case with possible implications for the classification of thyroid carcinomas

We describe the case of a 33-year-old woman with a thyroid carcinoma showing poorly differentiated (insular), anaplastic, and glandular features, the latter with extensive clear cell changes. Grossly, the well-circumscribed tumor nodule measured 3.6 cm in maximum dimension and was confined to the thyroid. Microscopically, the majority of the tumor was composed of well-defined "insular" nests showing microfollicular formation, high mitotic activity, and areas of necrosis. Other regions, as well as the intervening stroma of the insular nests, were characterized by highly atypical and pleomorphic stromal cells, extensive necrosis, and malignant cartilaginous nodules. Approximately 30% of the tumor was composed of diffuse glandular formations, each of which were lined by elongated, simple columnar cells with basally situated, mildly pleomorphic nuclei, clear supranuclear, periodic acid-Schiff + (and diastase sensitive) cytoplasm, empty lumens, and no myoepithelia or basement membranes. Immunohistochemically, the glandular elements displayed diffuse and strong positivity for thyroid transcription factor-1, bcl-2, and CAM 5.2, sparse positivity for thyroglobulin and Ki67, and diffuse but weak positivity for p53. Calcitonin was negative throughout the tumor. Karyotypic analysis of a primary culture showed a complex hypertriploid karyotype including structural abnormalities of chromosomes X, 1, 4, 6, 9, 13, and 14 in the majority of cells examined. This composite of histologic findings, especially the glandular patterns, is unusual and their prognostic significance is unclear. The patient is alive with no evidence of tumor recurrence or metastasis at 5 months follow-up. Overall, the morphologic and immunohistochemical properties of the glandular component suggests that they are less differentiated than well-differentiated carcinomas and are probably more differentiated than the insular component. This case supports the theory that the various primary carcinomas of the thyroid may represent points along a spectrum rather than distinct entities.

Clonal analysis of cutaneous fibrous histiocytoma (dermatofibroma)

BACKGROUND

Dermatofibroma (DF) or cutaneous fibrous histiocytoma is a common benign fibrohistiocytic lesion involving the dermis and subcutis. Histologically, it is subclassified into fibroblastic and histiocytoid forms. Its histogenesis is controversial. While often referred to as a neoplastic process, definite evidence of neoplasia in DF has been lacking. Alternatively, some authorities have suggested that DF is a fibrosing inflammatory process. Diagnostically, the most important question faced is the distinction from dermatofibrosarcoma protuberans (DFSP). Misdiagnosis can occur, as the early phase of DFSP can simulate DF, particularly the deep and cellular forms of DF.

METHODS

To address this issue, and to investigate whether DF is in fact a neoplasm, we evaluated 31 examples of DF of various histological types in female patients and assessed clonality by analyzing X-chromosome inactivation as indicated by the methylation status of the androgen receptor gene (HUMARA). Representative cases of DFSP were analyzed for comparison.

RESULTS

Among the selected 31 cases of DF, 24 cases provided intact DNA and informative polymorphism at the AR alleles, including one case of recurrent deep fibrous histiocytoma. Among these 24 cases, randomly inactivated AR alleles were observed in 17 cases including a deep, recurrent fibroblastic DF. A non-random inactivation at AR alleles was observed in seven cases, of which six cases showed either typical histiocytoid form of DF (four cases) or mixed cell types with predominant histiocytoid cell type (two cases). One fibroblastic DF also showed a monoclonal pattern. HUMARA analysis of DFSP revealed non-random inactivation of polymorphic AR alleles.

CONCLUSIONS

These findings suggest that DF is a heterogeneous process. Monoclonal genotype was found in DFs with histiocytoid or mixed type with predominant histiocytoid features, suggesting that histiocytoid cells probably represent the neoplastic component. The fibroblastic form of DF may represent a reactive fibroblastic proliferation. Alternatively, it may represent a true neoplasm whose neoplastic cell type has been obscured by prominent reactive fibroblastic component.

Factors affecting autopsy rates, autopsy request rates, and autopsy findings at a large academic medical center

Autopsy rates continue to decline in the United States. To assess the impact of various objective factors (time of death, day of death, age at death, patient gender, clinical service, and length of hospital stay) on the autopsy request rate, autopsy rate, successful request rate, and percentage of cases in which the autopsy examination added to or altered the clinical assessment of the patient, we prospectively studied all hospital deaths at a major academic medical center for the 3-year period from 1996 through 1998. The autopsy rate decreases significantly with patient age, both because of a decreasing request rate and because family members are less likely to grant permission. An autopsy is less likely to be requested for deaths in the emergency department or on general surgery services and most likely to be requested for fetal, medicine, cardiothoracic surgery, and pediatric deaths. Families more commonly grant permission for autopsy on fetal deaths, pediatric deaths, and emergency department deaths. Forty percent of autopsies reveal significant information about the patient's death beyond what was known premortem. This is least frequent among the fetal deaths, but relatively constant for adults of all ages. Patients who die in the emergency department are most likely to have significant unexpected findings at autopsy. Increasing the request rate for adult patients who die in the emergency department and on the medicine services will result in the greatest increase in information learned from autopsy.

Quality improvement on an academic autopsy service

CONTEXT

Autopsy rates continue to decline in the United States.

OBJECTIVE

Although many of the causes of this decline are external to pathology departments, we hypothesized that intradepartmental efforts to improve the quality of the service we provide to our clinical colleagues could increase our autopsy rate.

METHOD

We developed a multifaceted quality improvement program for our autopsy service aimed at increasing the visibility of the service, improving the service's reporting, and increasing the amount and quality of data available from the service.

SETTING

A large academic medical center that performs approximately 250 autopsies each year.

RESULTS

After implementation of our quality improvement program, the decline in our autopsy rate has not only stopped, but rates have even begun to increase. Additionally, physician satisfaction surveys conducted before and after implementation of our quality improvement initiatives showed an across-the-board improvement in clinician perception of the service.

CONCLUSION

Pathologists can and should be proactive in addressing the declining autopsy rate, rather than viewing it as someone else's problem or hoping that someone else will protect this important quality assurance tool for medical care.

Implementation of a practical digital imaging system for routine gross photography in an autopsy environment

BACKGROUND

The autopsy environment places stringent requirements on a digital imaging system. These requirements must be addressed if the system is to be functional, easy to use, and reliable.

DESIGN

After clearly defining the requirements for such a system, we implemented routine digital imaging in a busy academic autopsy suite.

RESULTS

The new technology was immediately accepted by both the resident staff and the technical staff. Although a 35-mm camera was always available for traditional photography, it was rarely used. An interesting side effect of implementing digital imaging was a nearly twofold increase in the number of images taken per autopsy case. The requirements, features, and utility of a digital imaging system are discussed.

CONCLUSION

Digital imaging in an autopsy environment can be both practical and cost-effective. It provides many advantages over traditional 35-mm photography and can be the first step toward numerous additional improved services.

Immunohistochemical distinction of ocular sebaceous carcinoma from basal cell and squamous cell carcinoma

BACKGROUND

Diagnosis of sebaceous carcinoma of the periorbital region is often delayed. Clinically, this lesion can mimic several inflammatory disorders. Histopathologically, it can mimic either squamous cell or basal cell carcinoma.

OBJECTIVE

To identify an immunohistochemical approach to assist in the diagnosis of periorbital sebaceous carcinoma.

METHOD

The immunohistochemical profiles of several cases of periorbital sebaceous, basal cell, and squamous cell carcinoma were examined.

RESULTS

Although at least focal epithelial membrane antigen (EMA) staining can effectively distinguish sebaceous carcinoma (10 of 11 were positive) from basal cell carcinoma (1 of 16 were positive), most squamous cell carcinomas examined were also focally EMA positive (11 of 14). However, Cam 5.2 reactivity was seen in most sebaceous carcinomas (8 of 11) but no squamous cell carcinomas (0 of 14). In addition, at least focal BRST-1 reactivity was also seen in most sebaceous carcinomas (7 of 11) but no basal cell carcinomas (0 of 16).

CONCLUSIONS

Periorbital sebaceous, basal cell, and squamous cell carcinomas have different immunohistochemical staining profiles; a panel of commonly available antibodies, including anti-EMA, BRST-1, and Cam 5.2, may help distinguish these diseases from each other when that distinction cannot be clearly made by light microscopy alone.

Exclusion of the stomatin, alpha-adducin and beta-adducin loci in a large kindred with dehydrated hereditary stomatocytosis

Defects in stomatin, alpha-adducin, and beta-adducin have been implicated in erythrocyte disorders of cation permeability. We performed linkage analysis of the genetic loci for these proteins in a large kindred with xerocytosis (dehydrated hereditary stomatocytosis). Using polymerase chain reaction-based genotyping techniques, all three loci are excluded as disease gene candidates.

Pigmented villonodular synovitis of the temporomandibular joint: diagnostic imaging and endovascular therapeutic embolization of a rare head and neck tumor

We report a case of pigmented villonodular synovitis involving the temporomandibular joint that presented as a rapidly growing tumor with extension through the skull base into the middle cranial fossa. The case is of interest not only because of the unusual extensive infiltration of this tumor but also because of the role modern diagnostic imaging and endovascular therapeutic techniques played in its diagnosis and management.

Utilization of an 86 bp exon generates a novel adducin isoform (beta 4) lacking the MARCKS homology domain

A novel isoform of beta-adducin has been amplified and characterized from a human bone marrow cDNA library (GenBank #U43959). This isoform arises from the insertion of an 86 bp alternatively spliced and previously unrecognized exon (now termed exon 15) within codon 581 of the human red blood cell beta-adducin sequence. This results in an insertion of 28 novel amino acids. The remainder of the red cell beta-adducin mRNA is then translated in a different reading frame, adding an additional 35 novel amino acids prior to the stop codon. This new isoform, thus, replaces beta 1-adducin sequence after residue 580 with a total of 63 new amino acids. Sequences from genomic clones of the human beta-adducin gene show that this alternate exon is flanked by splice consensus sequences and is appropriately located in the genomic map between exons encoding up-stream and down-stream sequences, thus defining a new exon. The COOH-terminus of this new isoform, which we designate beta 4, lacks a 22 amino acid lysine-rich sequence common to both the human red cell alpha- and beta-adducin subunits and homologous to a highly conserved region in MARCKS, a filamentous actin-cross linking protein regulated by protein kinase C and calcium/calmodulin. beta 4-adducin preserves a previously identified calmodulin binding domain. PCR analysis indicates that this new beta-adducin isoform is expressed in fetal brain and liver, bone marrow, and NT-2 (neuroepithelial) cells, but is not detected in several other tissues. We anticipate that this new beta 4 isoform of beta-adducin will display unique and tissue-specific functional properties.

Neuronal loss from the subthalamic nuclei in a patient with progressive chorea

We present a case of an 80-year-old man who developed a seizure disorder at age 66 and was treated with chronic phenytoin. In the last 3 years of his life, he developed multiple neurological deficits, including bilateral chorea, ataxic gait, sensory neuropathy, and progressive dementia. After death from pneumonia, autopsy examination of the patient's brain was most remarkable for a selective loss of neurons from both subthalamic nuclei and Purkinje cell loss in the cerebellum. This pattern of injury is consistent with a toxic process and does not fit previously characterized pathological syndromes known to be associated with movement disorders or dementia or both. Phenytoin has been shown to cause choreiform movements, peripheral neuropathy, and cognitive decline in some patients, but the pathological basis for these changes has not been elucidated. The patient's chorea was very likely the result of neuronal loss in the subthalamic nuclei, but causes for his dementia and neuropathy were not found. The pathological findings may represent either an unusual form of chronic phenytoin toxicity or a previously undescribed primary degenerative brain syndrome.

Reduced alpha-catenin and E-cadherin expression in breast cancer

BACKGROUND

The expression of the homotypic cell adhesion protein, E-cadherin, is reduced in many types of cancer. The loss of this protein may be associated with metastasis because alteration of its function is required for invasion in vitro, and decreased expression has been associated with more aggressive tumor behavior in vivo. It is likely that the loss of downstream effector elements in the cadherin adhesion cascade may also disrupt cell-cell interactions and thereby promote invasion, but direct evidence for this has been lacking. One such effector element is alpha-catenin, a cytoplasmic protein related to vinculin that is associated in vivo with E-cadherin.

EXPERIMENTAL DESIGN

In the present study, antibodies prepared to recombinant human alpha-catenin and recombinant human E-cadherin have been used to explore by immunocytochemistry the steady state levels of these proteins in a series of 26 cancers of the breast.

RESULTS

The expression of alpha-catenin was reduced or lost more frequently (81% of cases) than was the expression of E-cadherin (63% of cases). Cases with absent E-cadherin expression uniformly lacked alpha-catenin. Eight of the 26 patients (31%) had known metastatic disease at the time of biopsy; yet, all patients with normal alpha-catenin staining in their tumors were free of known metastatic disease (four patients).

CONCLUSIONS

Together with previous data on E-cadherin, these results suggest that reduced steady state levels of alpha-catenin may be a sensitive marker for disturbances in the adhesive function of the junctional complex and suggest that failure of at least one component of the cadherin-mediated cell-cell adhesion cascade is a common feature of breast, and presumably other, epithelial tumors.

Cardiogenic shock due to progression of cutaneous T-cell lymphoma

We describe a patient with progressive cutaneous T-cell lymphoma (CTCL) and development of subacute cardiac failure. Symptomatic lymphomatous involvement of the heart may be more common in patients with CTCL than in other lymphomas because the former is more likely to be associated with circulating tumor cells and hematogenous spread to the myocardium. No single symptom or sign is highly predictive of cardiac involvement, but unexplained tachyarrhythmias, conduction disturbances, low voltage on ECG, and unexplained cardiac enlargement should arouse clinical suspicion. Although echocardiography may be helpful in suggesting cardiac involvement, endomyocardial biopsy should be considered in patients with a reasonable chance of responding to chemotherapy or radiation.

Identification of functional regions on the tail of Acanthamoeba myosin-II using recombinant fusion proteins. II. Assembly properties of tails with NH2- and COOH-terminal deletions

We used purified fusion proteins containing parts of the Acanthamoeba myosin-II tail to localize those regions of the tail responsible for each of the three steps in the successive dimerization mechanism (Sinard, J. H., W. F. Stafford, and T. D. Pollard. 1989. J. Cell Biol. 107:1537-1547) for Acanthamoeba myosin-II minifiliment assembly. Fusion proteins containing the terminal approximately 90% of the myosin-II tail assemble normally, but deletions within the last 100 amino acids of the tail sequence alter or prevent assembly. The first step in minifilament assembly, formation of antiparallel dimers, requires the COOH-terminal approximately 30 amino acids that are thought to form a nonhelical domain at the end of the coiled-coil. The second step, formation of antiparallel tetramers, requires the last approximately 40 residues in the coiled-coil. The final step, the association of two antiparallel tetramers to form the completed octameric minifilament, requires residues approximately 40-70 from the end of the coiled-coil. A region of the tail near the junction with the heads is important for tight packing of the tails in the minifilaments. Divalent cations induce the lateral aggregation of minifilaments formed from native myosin-II or fusion proteins containing a nonmyosin "head," but under the same conditions fusion proteins composed essentially only of myosin tail sequences with very little nonmyosin sequences form paracrystals. The region of the tail necessary for this paracrystal formation lies NH2-terminal to amino acid residue 1,468 in the native myosin-II sequence.

Acanthamoeba myosin-II minifilaments assemble on a millisecond time scale with rate constants greater than those expected for a diffusion limited reaction

We have shown previously that Acanthamoeba myosin-II minifilaments assemble by three successive dimerization steps, forming, progressively, monomers, antiparallel dimers, antiparallel tetramers, and finally the full size octameric minifilament (Sinard, J. H., Stafford, W. F., and Pollard, T. D. (1989) J. Cell Biol. 109, 1537-1548). In the current study, we investigate the kinetics of the assembly of these minifilaments, initiating assembly by the rapid dilution of salt in a stopped-flow light scattering apparatus. The majority of the reaction is completed within 50 ms and is greater than 90% completed within 1 s. Assembly data over a greater than 6-fold myosin concentration range can be fit using the successive dimerization mechanism with a single set of rate constants. Second order rate constants for the initial steps in the assembly reaction exceed 10(8) M-1 s-1, and equilibrium dissociation constants predict a very low critical concentration, consistent with previous data. Other possible assembly mechanisms do not adequately fit all of the available data. Filament disassembly at 300 mM KCl is even more rapid, and there is both an increase in the dissociation rate constants and a decrease in the association rate constants with increasing KCl. Aggregation of minifilaments induced by Mg2+ is much slower and takes many minutes to reach equilibrium.