Progressive multifocal leukoencephalopathy during ixazomib-based chemotherapy

Progressive multifocal leukoencephalopathy (pml) is a rare demyelinating disease of the central nervous system that most often affects immunocompromised individuals. It is caused by the reactivation of the John Cunningham virus (jcv), which is found in latent form in the majority of adults. We describe a 59-year-old man with multiple myeloma who developed severe neurological deficits during treatment with ixazomib-based chemotherapy. A diagnosis of pml was established with gadolinium-enhanced magnetic resonance imaging (mri) and by detection of jcv in the cerebrospinal fluid. Despite cessation of chemotherapy and treatment with mirtazapine, he had an inexorable neurological decline and died two months after presenting to hospital. Multiple myeloma and its treatments can predispose patients to opportunistic infections including pml. Although there have been case reports of pml in patients with multiple myeloma treated with bortezomib (a different proteosome inhibitor), this is, to our knowledge, the first documented case of pml in a patient treated with a regimen that includes ixazomib.

Nontraumatic Acute Anterior Cord Syndrome Caused by Cervical Disc Herniation after Napping with Neck Extension

Nontraumatic acute anterior cord syndrome caused by disc herniation occurring in the cervical spine is rare. A 39-year-old man presented with a sharp burning pain in bilateral upper limbs and progressive paraplegia after a nap with neck extension. He had impaired sensation of pain and temperature with preservation of proprioception and light touch below the C6 level. The magnetic resonance imaging showed focal hyperintensity of the anterior cord at the C5-C7 level and central herniation of C5-6 and C6-7 discs. An anterior discectomy of C5-6 and C6-7 was conducted because of the poor response to a high dose of steroid. A postoperative intensive rehabilitation treatment was also performed. The patient showed significant improvement in motor and sensory function three months postoperatively. Long-term repetitive neck extension should be avoided because it may be a risk for degenerative spondylotic change and cord compression disorders. Surgical intervention should be considered in a patient with anterior cord syndrome associated with nontraumatic cervical disc herniation. (Hong Kong j.emerg.med. 2013;20:389-391)

A Unique Hairy Cell Leukemia Variant

A 65-year-old woman presented with easy bruising, left upper quadrant pain, decreased appetite, and weight loss. She had splenomegaly and lymphocytosis (lymphocyte count of 11.6 × 10(9)/l), with remarkably abnormal appearing morphology. Her hemoglobin and platelet counts were normal. Peripheral blood flow cytometry revealed a monoclonal B-cell population expressing CD11c, CD25, CD19, CD20, and CD103. An initial diagnosis of hairy cell leukemia (HCL) was made, and the patient was treated with a standard 5-day course of cladribine. However, her lymphocytosis improved transiently, with a relapse 4 months later. There was no improvement in her splenomegaly. An HCL variant (HCL-v) was considered based on her resistance to treatment with a purine nucleoside analog. A subsequent splenectomy improved symptoms. Two years after, the patient suffered a relapse and underwent 6 cycles of CHOP-R (cyclophosphamide, hydroxydaunomycin, oncovin, prednisone, and rituximab), achieving partial remission. While under observation, she progressed with lymphocytosis 6 months later and was treated with pentostatin. There was no significant improvement in her disease, and she died 8 weeks following treatment initiation. HCL-v is a clinically more aggressive mature B-cell lymphoma than HCL with worse splenomegaly, higher lymphocyte counts, and resistance to typical HCL therapy with purine nucleoside analogs. Early recognition of HCL-v in the history, physical examination, and investigations with morphology and flow cytometry is key to patient management. Further, as in our case of HCL-v, cell morphology can be distinctly atypical, with large nucleoli and extremely convoluted nuclei. The distinction between HCL and HCL-v is important as HCL-v patients require more aggressive therapy and closer follow-up.

Randomized double-blind safety comparison of intravenous iron dextran versus iron sucrose in an adult non-hemodialysis outpatient population: A feasibility study

Background

Intravenous iron therapy is a treatment option for iron deficient patients who are intolerant to oral iron or where oral iron is ineffective, but with possible adverse effects. Currently, prospective studies comparing different intravenous iron formulations are needed to determine safety and efficacy of these agents.

Methods

We conducted a prospective, double-blind, randomized controlled trial (RCT) to assess the feasibility of a trial comparing the safety of high molecular weight intravenous iron dextran, Infufer®, with intravenous iron sucrose, Venofer®, in non-hemodialysis adult outpatients. Primary outcome was the occurrence of immediate severe drug reactions.

Results

We enrolled 143 patients in a one-year period. Overall, 45/143 (31.5 %) patients (20 iron dextran, 25 iron sucrose) developed 48 infusion reactions (14 immediate, 28 delayed, and 3 both). The risk of an immediate reaction was similar in both groups, 9/73 (12.3 %) iron dextran versus 8/70 (11.4 %) iron sucrose, RR = 0.93 (95 % CI; 0.38 to 2.27). The risk of a delayed reaction was significantly higher in the iron sucrose group 22/70 (31.4 %) versus the iron dextran group 9/73 (12.3 %), RR = 2.55 (95 % CI; 1.26 to 5.15; p = 0.0078).

Conclusion

In this limited feasibility study, no major differences in immediate reactions were seen, but a significantly higher number of delayed reactions were seen in the iron sucrose group. Further, under our assumptions and design a full RCT to evaluate the safety of different intravenous iron preparations is not feasible. Future studies should consider modifying the clinical outcomes, utilize multiple centers, and consider other emerging parenteral iron formulations. (ClinicalTrials.gov NCT005936197 January 3, 2008).

Use of n-of-1 (single patient) trials to assess the effect of age of transfused blood on health-related quality of life in transfusion-dependent patients

BACKGROUND

The impact of age of red blood cells on health-related quality of life (HRQL) in patients who require chronic transfusions is not known. We assessed this using n-of-1 trials in patient populations where large randomized trials have not been done to date.

STUDY DESIGN AND METHODS

Chronically transfusion-dependent adult patients were randomly assigned over time to four fresh (<7 days of storage) and four standard-issue (up to 42 days of storage) blood transfusions in prospective double-blinded multicrossover studies (n-of-1 trials). HRQL questionnaires were completed before and at 24 hours after each transfusion. Hemoglobin (Hb) levels were measured before each subsequent transfusion.

RESULTS

Twenty transfusion-dependent patients were enrolled, of whom nine (five myelodysplastic syndromes, two myelofibrosis, one β-thalassemia major, one Diamond-Blackfan anemia) completed at least six transfusions. Mean ages of fresh and standard-issue blood transfused were 4.0 and 23.2 days, respectively. There were no significant differences in the effect of standard and fresh blood on follow-up Hb levels or the eight HRQL dimensions assessed in all analyses.

CONCLUSIONS

In chronically transfused patients, there were no significant differences in HRQL or Hb levels between fresh versus standard blood. While larger trials are needed, these results support current practices in hospital blood transfusion laboratories using a first-in, first-out model of blood utilization for these transfusion-dependent patients. Use of n-of-1 trials to determine the benefits of transfusions in single patients appears to be feasible.

Incidence and natural history of intravenous immunoglobulin-induced aseptic meningitis: a retrospective review at a single tertiary care center

BACKGROUND

Aseptic meningitis is a rare but significant complication of intravenous immunoglobulin (IVIG) therapy. The majority of literature is limited to case reports, so the true incidence of this complication is uncertain.

STUDY DESIGN AND METHODS

A retrospective review of all cases of IVIG-associated adverse transfusion reactions was performed at London Health Sciences Centre (LHSC) from January 1, 2008, to December 31, 2013. All reported transfusion reactions were evaluated to identify cases of aseptic meningitis due to IVIG. All documented IVIG infusions and lumbar punctures performed during the study period were reviewed; patients with both interventions were identified and further chart review was performed to identify aseptic meningitis.

RESULTS

During our study period, 1324 unique patients received a total of 11,907 IVIG infusions (554,566 g) for various conditions. Eight cases of aseptic meningitis were identified, suggesting an overall incidence of 0.60% for all patients and 0.067% for all IVIG infusions. Patients presented with symptoms within 24 to 48 hours of the infusion and were treated with antibiotics initially. The reactions were self-limited, as symptoms self-resolved within 5 to 7 days. Treatment was supportive, with subsequent IVIG infusions likely requiring preinfusion medication or possibly a switch in product formulation.

CONCLUSION

This review of IVIG-induced aseptic meningitis over a 6-year period identifies a more robust estimate of incidence and risk of 0.60% and 0.067% for all patients and infusions, respectively. Given that this complication can mimic infectious meningitis and cause considerable morbidity, physicians need to be aware of this rare but important condition.

A case of transfusion independence in a patient with myelodysplastic syndrome using deferasirox, sustained for two years after stopping therapy

Patients with myelodysplastic syndrome (mds) experience clinical complications related to progressive marrow failure and have an increased risk of developing acute myeloid leukemia. Frequent red blood cell transfusion can lead to clinical iron overload and is associated with decreased survival in mds patients. Iron chelation therapy reduces markers of iron overload and prevents end-organ damage. Here, we present the case of a patient with low-risk mds with transfusional iron overload. He was treated for 2 years with an oral iron chelator, deferasirox, and after 12 months of treatment, he experienced a hemoglobin increase of more than 50 g/L, becoming transfusion-independent. He has remained transfusion-independent, with a normal hemoglobin level, for more than 2 years since stopping chelation therapy. Hematologic and erythroid responses have previously been reported in mds patients treated with iron chelation. The durability of our patient's response suggests that iron chelation might alter the natural history of mds in some patients.

Intravenous Immunoglobulin (IVIg) Utilization in Immune Thrombocytopenia (ITP): A Multi-Center, Retrospective Review

Introduction

Intravenous immunoglobulin (IVIg) is an immune thrombocytopenia (ITP) therapy, which is associated with toxicities, limited availability, increasing utilization, and high cost. This study aimed to assess short- and long-term IVIg utilization in patients with ITP at two tertiary care centers in Ontario, Canada, to determine the proportion of IVIg used in ITP compared with all usage, and to forecast IVIg demand in ITP.

Methods

Records from all adult ITP patients who received IVIg between January 1, 2003, and September 30, 2012, at Hamilton Health Sciences and London Health Sciences Centre were reviewed retrospectively.

Results

During the study period, 383 adult ITP patients (mean age 51.3 years) received a total of 2,098 IVIg infusions (London 547 infusions in 150 patients; Hamilton 1,551 infusions in 233 patients). ITP accounted for 5.6 and 9.1 % of all IVIg usage in London and Hamilton, respectively. The treatments included 264 (53.7 %) acute, 172 (35.0 %) short-term, and 56 (11.4 %) long-term treatments. The amounts of IVIg used for short- and long-term treatment of ITP are forecasted to be approximately 5,000 and 11,000 g per year, respectively, up to 2018. Together, these two centers represent 19.9 % of the provincial IVIg utilization. Assuming similar patient populations and practice patterns in Ontario, the overall provincial cost of IVIg use in ITP may be as high as $5 million annually.

Conclusion

Short- and long-term IVIg utilization for ITP will remain an expensive resource within the Ontario provincial health care system. Physicians and policy makers should reflect on the impact of treating ITP with IVIg and should consider alternatives, where appropriate, to improve patient quality of life and decrease economic costs.

Electronic supplementary material

The online version of this article (doi:10.1007/s40801-015-0009-6) contains supplementary material, which is available to authorized users.

Response to "Need to minimize bias when surveying patient attitudes to stopping cml treatment"

We thank Villemagne et al. for their comments, and we will address some of the issues that they raised.[...]

Study of Octaplex dosing accuracy: an in vitro analysis

Prothrombin complex concentrates (PCC) are recommended for urgent warfarin reversal. However, disagreement exists regarding the proper dosing strategy (i.e. fixed vs. weight-based). We measured the in vitro effect of PCC dosing on international normalised ratio (INR) and factor activity. Plasma from warfarin-anticoagulated patients with stable INRs was collected. PCC doses of 1,000, 2,000 and 3,000 IU were added to the samples, and INR and factor activity were analysed before and after PCC. Twenty-three of thirty subjects enrolled had complete data for analysis. INRs were below 1.5 in all samples post-1,000 IU, and decreased further with subsequent doses (p<0.001). Factors II, VII, and X increased with consecutive doses (p<0.01). Linear correlation was seen between INR and factors II, VII and X. Factor IX did not increase consistently nor show correlation with INR reversal. Weight-based dosing was then estimated; INRs were all <1.2 (0.9-1.2) and activity >0.50 IU for factors II, VII and X (0.96-1.52, 0.51-1.45 and 0.81-1.38, respectively). Factor IX did not uniformly correct above 0.50 IU (0.31-1.31). We confirm in vitro that 1,000 IU of Octaplex(®) is able to correct INR to <1.5 but factors were not uniformly >0.50 IU until 2,000 IU, and not >1.00 IU until 3,000 IU. This suggests that INR correction alone may not accurately reflect factor activity, and lends support for weight-based dosing.

Mediastinal choriocarcinoma masquerading as relapsed hodgkin lymphoma

Primary mediastinal choriocarcinoma is a rare extragonadal germ cell malignancy. We describe the first case of a patient who developed mediastinal choriocarcinoma after treatment for Hodgkin lymphoma (HL). A 25-year-old man with classic HL, nodular sclerosis subtype, underwent treatment with splenectomy followed by radiation therapy. Unfortunately, his disease relapsed with a paraspinal mass, and he was subsequently treated with MOPP (mechlorethamine, Oncovin, procarbazine, and prednisone) alternating with ABVD (Adriamycin, bleomycin, vinblastine, and dacarbazine). He achieved a complete remission after 6 cycles. Ten years after treatment, the patient presented with a persistent cough, haemoptysis, right supraclavicular lymphadenopathy, and weight loss. His chest X-ray showed opacification of the lower right hemithorax with a widened mediastinum. Given unresponsiveness to several antibiotics and lack of evidence for lung volume loss, there were concerns over lung infiltration with relapsed lymphoma. Transbronchial fine needle aspiration biopsy suggested recurrence of his HL. MOPP alternating with ABVD was again given. Due to disease progression, brachytherapy as well as a cocktail of dexamethasone, cytarabine, and cisplatin were also tried. However, on a subsequent excisional lymph node biopsy, it turned out that the tumour was in fact choriocarcinoma and not relapsed HL. Unfortunately, despite aggressive therapy, the patient's disease rapidly progressed, and he died within 2 weeks.

Analysis and comparison of sleeping posture classification methods using pressure sensitive bed system

Pressure ulcers are common problems for bedridden patients. Caregivers need to reposition the sleeping posture of a patient every two hours in order to reduce the risk of getting ulcers. This study presents the use of Kurtosis and skewness estimation, principal component analysis (PCA) and support vector machines (SVMs) for sleeping posture classification using cost-effective pressure sensitive mattress that can help caregivers to make correct sleeping posture changes for the prevention of pressure ulcers.

Tumor suppression by phospholipase C-beta3 via SHP-1-mediated dephosphorylation of Stat5

Given its catalytic activity to generate diacylglycerol and inositol 1,4,5-trisphosphate, phospholipase C (PLC) is implicated in promoting cell growth. However, we found that PLC-beta3-deficient mice develop myeloproliferative disease, lymphoma, and other tumors. The mutant mice have increased numbers of hematopoietic stem cells with increased proliferative, survival, and myeloid-differentiative abilities. These properties are dependent on Stat5 and can be antagonized by the protein phosphatase SHP-1. Stat5-dependent cooperative transformation by active c-Myc and PLC-beta3 deficiency was suggested in mouse lymphomas in PLC-beta3(-/-) and in Emicro-myc;PLC-beta3(+/-) mice and human Burkitt's lymphoma cells. The same mechanism for malignant transformation seems to be operative in other human lymphoid and myeloid malignancies. Thus, PLC-beta3 is likely a tumor suppressor.

Recombinant activated factor VII in the treatment of non-haemophilia patients: physician under-reporting of thromboembolic adverse events

The objective of this study was to determine if clinically important thromboembolic adverse events (TAEs) because of recombinant activated factor VII (rFVIIa) administration are being under-reported. rFVIIa is a potent haemostatic agent with a short half-life of 2.6 h that is increasingly used in 'off-label' situations. Retrospective review of 94 patients who received rFVIIa during 1 January 2003 to 30 June 2007 was carried out at a tertiary care centre. Sixty-nine patients, 32 females and 37 males, mean age 55 years (18-84 years), satisfied study criteria of off-label usage. This was a high-risk population with 33 (48%) deaths. A mean dose of 8.2 mg (2.4-19.2 mg) was administered in two average divided doses. Thirty-six potential TAEs were identified in 29 patients, and of these, 12 patients had TAEs deemed to be rFVIIa related and were identified on average 8.8 days after exposure to rFVIIa. Forty-eight (70%) physician questionnaires were completed; however, no TAEs were reported in these questionnaires or on chart review. Potential clinically significant TAEs are being under-reported by treating physicians. Until further evidence, we suggest the urgent need to develop consensus recommendations for utilization and required follow up to monitor the safety of rFVIIa and that at a minimum, all use of rFVIIa should be regulated through a gate-keeping mechanism that ensures adherence to these policies. Furthermore, prospective registries and trials are necessary to evaluate the efficacy and safety of rFVIIa in off-label settings.

Hodgkin lymphoma with cutaneous involvement

We report a case of a 54-year-old previously healthy man with Hodgkin lymphoma who presented initially with a solitary cutaneous ulcer. Unlike non-Hodgkin lymphoma subtypes, skin involvement of Hodgkin lymphoma is extremely rare. Furthermore, the prognosis of Hodgkin lymphoma with skin infiltration is felt to be extremely poor. Contrary to other reports, this case demonstrates that a good response with standard therapy is possible.

Treatment of acquired factor X inhibitor by plasma exchange with concomitant intravenous immunoglobulin and corticosteroids

A patient with spontaneous hemorrhage from multiple body sites was found to have markedly prolonged international normalized ratio (INR) and activated partial thromboplastin times (aPTT) with incomplete correction of aPTT on mixing studies using normal plasma. The cause of this severe hemorrhage was due to a specific factor X inhibitor. No underlying or associated diseases were found. Initial treatment with fresh frozen plasma, vitamin K, and recombinant activated factor VII (rFVIIa) was unsuccessful. However, therapy utilizing plasma exchange with concomitant intravenous immunoglobulin and corticosteroids resulted in a rapid and sustained normalization of factor X levels with a clinical hemostatic response.

Evaluation of optimal cerebral perfusion pressure in severe traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability. In the 2000 guidelines, one of the suggestions for TBI treatment was to maintain cerebral perfusion pressure (CPP) < or = 70 mmHg. But in the 2003 guidelines, the suggestion was changed to < or = 60 mmHg. There have been some discrepancies of opinions about this recommendation in recent publications. In this study, we retrospectively reviewed 305 severe TBI (STBI) patients with Glasgow Coma Scales (GCS) < or = 8 between January 1, 2002 and March 31, 2003. The study group was stratified according to use or nonuse of intracranial pressure (ICP) monitoring, ICP levels, ages, and GCS levels in order to test the correlation between CCP and the prognosis. The patients < 50-year-old, with higher GCS level, with ICP monitoring, and with ICP levels < 20 mmHg had lower mortality rates and better prognosis (GOS) (p < 0.05 or 0.001). The patients in the GCS 3-5 subgroup had a significantly lower mortality and better prognosis if the CPP value was maintained higher than 70 mmHg (p < 0.05) The optimal CPP maintained < or = 60 mmHg did not fit in all STBI patients. Our study concludes that it is critical to maintain CPP substantially higher in lower GCS level patients.

Integration of hepatitis B virus containing mutations in the core promoter/X gene in patients with hepatocellular carcinoma

Integration of hepatitis B virus is thought to be an essential step in hepatitis B virus associated hepatocarcinogenesis. Mutations at nucleotides 1762 and 1764 in the hepatitis B virus, within a sequence encoding both the core promoter gene and the X gene, have been found frequently in patients with hepatocellular carcinoma. However, integration of these mutant sequences has not been reported to date.

METHODS

A 228-base pair segment of the hepatitis B virus core promoter gene was amplified from hepatocellular carcinomas and adjacent non-tumourous liver tissue by nested PCR and sequenced. Integration of hepatitis B virus into human genomic DNA was investigated using the 'genome walking' method.

RESULTS

Point mutations were found in both hepatitis B virus nucleotides 1762 and 1764 in 8 of 14 hepatocellular carcinoma tissues (57%) and in 11 of 14 adjacent non-tumourous liver tissues (79%). Three patients were evaluated using the 'genome walking' method; all were found to have hepatitis B virus DNA integrated in their hepatocellular carcinoma (two patients) and/or in their non-tumourous liver tissue (three patients). Integration occurred in all tissues near host genomic sites that are prone to integration. Hepatitis B virus was integrated at or near the hepatitis B virus DR1 site in all samples, and all contained truncated X gene sequences that have been reported to be capable of producing fusion transcripts with transactivation potential.

CONCLUSIONS

Integrated hepatitis B virus DNA containing core promoter mutations at nucleotides 1762 and 1764 was found in hepatocellular carcinoma and/or adjacent non-tumourous liver tissue of three patients. These findings leave open the possibility that insertional mutagenesis or transactivation by fusion transcripts resulting from hepatitis B virus integration could play a role in hepatocarcinogenesis in some patients.

Molecular and serological aspects of HBsAg-negative hepatitis B virus infections in North America

A few hepatitis B virus (HBV) infections are characterized by the presence of HBV DNA in serum or liver tissue, or both, in the absence of detectable hepatitis B surface antigen (HBsAg) in serum. However, such infections have rarely been described previously in North American patients. In the present study, 31 hepatocellular carcinoma (HCC) patients from the United States and Canada who had no detectable HBsAg in their serum were studied. In these 31 HBsAg-negative HCC patients, HBV DNA was detected in HCC and/or in adjacent nontumorous liver tissue using nested polymerase chain reaction (PCR) in 5/9 (56%) patients from the United States and in 12/22 (55%) from Canada. The 17 HBV DNA-positive/HBsAg-negative patients from the United States and Canada included 9 without any serological markers for HBV and 8 with detectable antibodies to hepatitis B core antigen. In these patients, HBV genotype C was the most prevalent genotype (11/17; 64%). HBV genotypes have not been previously reported in HCC patients from North America. Replicative intermediate forms of HBV (covalently closed circular HBV DNA) were detected in 2/17 (12%) HBV DNA-positive/HBsAg-negative patients, indicating that at least two of these patients had actively replicating HBV infections. The use of tests to detect HBV DNA permitted the identification of HBV infections in HBsAg-negative HCC patients from North America. Among these patients, those with antibody to hepatitis C virus (HCV) would otherwise have been designated "HCV-associated HCCs" based on serological tests alone. These findings provide a new perspective on determining the possible viral etiologies of HCCs in North America.

Pulmonary membrane diffusing capacity and capillary blood volume measured during exercise from nitric oxide uptake

STUDY OBJECTIVES

To validate lung diffusing capacity for nitric oxide (DLNO) as an index of conductance of the alveolar-capillary membrane during exercise, we compared DLNO to lung diffusing capacity for carbon monoxide (DLCO) and pulmonary membrane diffusing capacity for carbon monoxide (DMCO), and compared pulmonary capillary blood volume (Vc) calculated by two methods.

SETTING AND PARTICIPANTS

The study was performed at a university medical center involving 12 nonsmoking healthy volunteers (age range, 23 to 79 years). DLCO, DLNO, cardiac output (c), and lung volume were measured simultaneously at rest and during graded ergometer exercise by a rebreathing technique. Pulmonary membrane diffusing capacity and Vc were compared by (1) the classic technique of Roughton and Forster from DLCO measured at two alveolar oxygen tension (PAO(2)) levels, and (2) from DLNO and DLCO assuming negligible erythrocyte resistance to nitric oxide (NO) uptake, ie, DLNO approximately equal to pulmonary membrane diffusing capacity for nitric oxide.

RESULTS

In all subjects, DLNO increased linearly from rest to exercise; age, c, and lung volume were the major determinants of DLNO by stepwise regression analysis. The DLNO/DLCO ratio averaged 3.98 +/- 0.38 (+/- SD) and the DLNO/DMCO ratio averaged 2.49 +/- 0.28 irrespective of exercise intensity. Changing PAO(2) did not alter DLNO. Brief exposure to 40 ppm of inhaled NO during 16 s of rebreathing did not alter either DLCO or c. Estimates of pulmonary membrane diffusing capacity and Vc by the two methods showed a strong correlation.

CONCLUSION

Results support DLNO as a direct measure of pulmonary membrane diffusing capacity, allowing the estimation of Vc in a single rebreathing maneuver during exercise. The DLNO-DLCO rebreathing technique can be applied clinically in the investigation of pulmonary microvascular regulation.

Preventing mediastinal shift after pneumonectomy impairs regenerative alveolar tissue growth

To examine the effects of mechanical lung strain on regenerative growth of alveolar septal tissue after pneumonectomy (PNX), we replaced the right lungs of adult dogs with a custom-shaped inflatable silicone prosthesis. The prosthesis was either inflated (Inf) to maintain the mediastinum at the midline or deflated to allow mediastinal shift. The animals were euthanized approximately 15 mo later, and the lungs were fixed at a constant distending pressure. With the Inf prostheses, lung expansion, alveolar septal tissue volumes, surface areas, and diffusing capacity of the tissue-plasma barrier were significantly lower than with the deflated prostheses; the expected post-PNX tissue responses were impaired by 30-60%. Capillary blood volume was significantly higher with Inf prostheses, consistent with microvascular congestion. Measurements in the Inf group remained consistently and significantly higher than those expected for a normal left lung, indicating persistence of partial compensation. In one dog, delayed deflation of the prosthesis 9-10 mo after PNX led to vigorous lung expansion and septal tissue growth, particularly of type II epithelial cells. We conclude that mechanical lung strain is a major signal for regenerative lung growth; however, other signals are also implicated, accounting for a significant fraction of the compensatory response to PNX.