Protein, lipid and water organization in bacteriorhodopsin crystals: a molecular view of the purple membrane at 1.9 A resolution

BACKGROUND

Bacteriorhodopsin (bR) from Halobacterium salinarum is a proton pump that converts the energy of light into a proton gradient that drives ATP synthesis. The protein comprises seven transmembrane helices and in vivo is organized into purple patches, in which bR and lipids form a crystalline two-dimensional array. Upon absorption of a photon, retinal, which is covalently bound to Lys216 via a Schiff base, is isomerized to a 13-cis,15-anti configuration. This initiates a sequence of events - the photocycle - during which a proton is transferred from the Schiff base to Asp85, followed by proton release into the extracellular medium and reprotonation from the cytoplasmic side.

RESULTS

The structure of bR in the ground state was solved to 1.9 A resolution from non-twinned crystals grown in a lipidic cubic phase. The structure reveals eight well-ordered water molecules in the extracellular half of the putative proton translocation pathway. The water molecules form a continuous hydrogen-bond network from the Schiff-base nitrogen (Lys216) to Glu194 and Glu204 and includes residues Asp85, Asp212 and Arg82. This network is involved both in proton translocation occurring during the photocycle, as well as in stabilizing the structure of the ground state. Nine lipid phytanyl moieties could be modeled into the electron-density maps. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis of single crystals demonstrated the presence of four different charged lipid species.

CONCLUSIONS

The structure of protein, lipid and water molecules in the crystals represents the functional entity of bR in the purple membrane of the bacteria at atomic resolution. Proton translocation from the Schiff base to the extracellular medium is mediated by a hydrogen-bond network that involves charged residues and water molecules.

Early childhood MRI findings in complex partial seizures and hippocampal sclerosis

Magnetic resonance imaging (MRI) was performed on an infant with typical complex partial seizures. Visual analysis revealed MRI signs of left hippocampal sclerosis (HS) at an age of 9 months. Morphometric data including volumetry and relaxometry confirming the diagnosis are shown. This is the first report of an infant younger than 2 years with typical MRI findings including morphometric data on HS.

Systematic characterisation of disease associated balanced chromosome rearrangements by FISH: cytogenetically and genetically anchored YACs identify microdeletions and candidate regions for mental retardation genes

Disease associated balanced chromosome rearrangements (DBCRs) have been instrumental in the isolation of many disease genes. To facilitate the molecular cytogenetic characterisation of DBCRs, we have generated a set of >1200 non-chimeric, cytogenetically and genetically anchored CEPH YACs, on average one per 3 cM, spaced over the entire human genome. By fluorescence in situ hybridisation (FISH), we have performed a systematic search for YACs spanning translocation breakpoints. Patients with DBCRs and either syndromic or non-syndromic mental retardation (MR) were ascertained through the Mendelian Cytogenetics Network (MCN), a collaborative effort of, at present, 270 cytogenetic laboratories throughout the world. In this pilot study, we have characterised 10 different MR associated chromosome regions delineating candidate regions for MR. Five of these regions are narrowed to breakpoint spanning YACs, three of which are located on chromosomes 13q21, 13q22, and 13q32, respectively, one on chromosome 4p14, and one on 6q25. In two out of six DBCRs, we found cytogenetically cryptic deletions of 3-5 Mb on one or both translocation chromosomes. Thus, cryptic deletions may be an important cause of disease in seemingly balanced chromosome rearrangements that are associated with a disease phenotype. Our region specific FISH probes, which are available to MCN members, can be a powerful tool in clinical cytogenetics and positional cloning.

Regional cerebral blood flow single-photon emission tomography with 99mTc-HMPAO and the acetazolamide test in the evaluation of vascular and Alzheimer's dementia

The diagnostic potential of technetium-99m hexamethylpropylene amine oxime (HMPAO) following systemic administration of the cerebral vasodilator acetazolamide (acetazolamide test) was evaluated by regional cerebral blood flow (rCBF) single-photon emission tomography (SPET) in patients with Alzheimer's disease (AD) or vascular dementia (VD). An initial, high-resolution SPET study was performed with 99mTc-HMPAO, and after 2 days the patients were re-evaluated with 99mTc-HMPAO following systemic administration of acetazolamide. Reconstructed SPET slices were evaluated visually and semiquantitatively by a semi-automatic rCBF map method. When 99mTc-HMPAO alone was used, bilateral hypoperfusion was found in the temporal and/or parietal regions in 33% (6/18) of the VD patients and in 70% (23/33) of the AD patients. The corresponding data obtained by quantitative evaluation were 41% (7/17) and 71% (15/21), respectively. The vascular reserve capacity, as determined with the acetazolamide test, was preserved visually in 22% (4/18) and quantitatively in 29% (5/17) of the VD patients, but in 73% (24/33) and 76% (16/21) of the AD patients. The differences in the perfusion patterns between the VD and AD patients were statistically significant (P<0.01, Fischer's exact test). Of the VD patients with hypoperfusion (bilateral temporal and/or parietal), 4/6 (67%, visual evaluation) and 4/7 (57%, quantitative evaluation) had a decreased vascular reserve capacity as determined with the acetazolamide test. In the AD group of patients the corresponding results were 3/23 (13%) and 4/15 (27%). It is concluded that the acetazolamide test is promising in rCBF SPET to differentiate VD from AD.

p34cdc2 in invasive breast cancer: relationship to DNA content, Ki67 index and c-erbB-2 expression

AIMS

One-hundred and eighty-eight cases of human mammary carcinoma were examined immunohistochemically for their expression of Ki67, p34cdc2 and c-erbB-2. DNA image cytometry was performed to evaluate DNA ploidy, Auer type, S-phase fraction (SPF), 5c exceeding rate (5cER) and 2c deviation index (2cDI).

METHODS AND RESULTS

One-hundred and sixty-eight cases were invasive ductal carcinomas, 20 were of invasive lobular type. Routinely assessed oestrogen and progesterone receptor scores were available. The results were analysed statistically in comparison to tumour type, histopathological grade, lymph node status, menopausal status, patient age and overall survival. Ki67 (P < 0.002) and c-erbB-2 (P < 0.0001) correlated well with overall survival (P < 0.0008) and grade (P < 0.038) but not with lymph node status and tumour type. p34cdc2 showed a trend towards a positive correlation with Ki67 (P < 0.058) and a significant negative correlation with receptor status (P < 0.008) but with none of the other parameters examined.

CONCLUSIONS

No association between the DNA measured parameters (Auer type, SPF, 5cER and 2cDI) and survival was found. Our results suggest that c-erbB-2 and Ki67 are parameters which might, in combination with receptor status, help to define subgroups with different outcomes.

Inhibitory effects of mesial temporal partial seizures onto frontal neocortical structures

PURPOSE

A retrospective evaluation of the ictal temporal tracer uptake and the perfusion pattern in other neo- and subcortical structures was performed to define typical extratemporal changes of rCBF that might further aid the differentiation of temporal and extratemporal seizures.

METHOD

Ictal and interictal rCBF brain SPECT studies were done in 17 patients with seizures of mesial temporal onset according to scalp electroencephalography (EEG) and electrocorticography (ECoG) using 99mTc-ECD. Except for hippocampal sclerosis/atrophy, which was found in 11/17 patients, no morphologic anomalies were detected by MRI. Ictal tracer injections were given immediately after the onset of the seizure according to continuous video-EEG monitoring. The injection latency was two to twenty seconds. The data acquisition was done 45 minutes after the tracer injection using an annular crystal system (Ceraspect, DSI). In 15 patients a semiquantitative ROI-analysis of the tracer uptake in temporal and frontal regions could be obtained.

RESULTS

All ictal studies correctly localised the affected temporal lobe. A detection of the epileptogenic focus itself was successful in 59% of patients while in the remaining patients the maximum of tracer uptake was not found to be located in the mesial temporal lobe only. In contrast to all other cerebral structures, only within the ipsilateral basal frontal cortex a frequent reaction to the temporal seizure was found. The basal frontal cortex ipsilateral to the affected temporal lobe showed a reduction of tracer uptake between the ictal and interictal study in 82% of patients which was semiquantitatively significant using a paired t-test (p < 0.05). Other neo- or subcortical structures showed inconsistent results.

CONCLUSION

Secondary involvement of neocortical temporal structures in ictal rCBF-SPECT with 99mTc-ECD occurs early and focal maxima of tracer uptake within the temporal lobe do not necessarily represent the epileptogenic focus itself. Seizures of mesial temporal origin did not activate but frequently depressed the ipsilateral basal frontal tracer uptake during the early ictal phase. This phenomenon may account for some aspects of the clinical appearance of mesial temporal seizures.

Redifferentiation therapy-induced radioiodine uptake in thyroid cancer

Due to a dedifferentiation of tumor cells, some thyroid carcinomas lose their capability for radioiodine (RI) concentration. This phenomenon is associated with a worse prognosis and prevents effective treatment. Retinoic acid (RA) is known to induce redifferentiation in various kinds of tumors and has been used recently in thyroid cancer.

METHODS

Twelve patients (9 women, 3 men) with 6 papillary, 4 follicular and 2 mixed-cell type tumors (including 4 Hurthle cell carcinomas) were treated orally with RA (dose: 1.18 +/- 0.37 mg/kg body weight) for at least 2 mo before RI therapy. None of the patients could be treated with any other modality (RI, surgery, external radiation) when RA administration was started. Initially, clinically important tumor sites did not take up significant amounts of RI. Changes of RI uptake and thyroglobulin (Tg) serum values were determined. Glucose metabolism was followed with fluorodeoxyglucose (FDG) PET imaging in 10 patients before and in 5 patients after RA treatment.

RESULTS

In 2 patients, a significant RI uptake was induced by RA, and in another 3 patients a faint RI uptake was achieved (responder group). In 7 patients, no change of RI uptake was observed (nonresponder group). Median Tg was increased from 105-840 microg/liter during RA therapy in the responder group, which was significantly higher than the nonresponder group (173-134 microg/liter). FDG PET was positive in all 10 patients before RA therapy. PET showed variable patterns of changes (increase/decrease/disappearance) in glucose consumption related to RA response.

CONCLUSION

RA can induce RI uptake in some patients with RI negative thyroid carcinoma tumor sites. Response to RA is associated with a significantly higher increase of Tg, suggesting that a restoration of Tg synthesis can be addressed as a redifferentiation parameter in these patients.

Redifferentiation therapy with retinoic acid in follicular thyroid cancer

We report on a patient with a follicular Hurthle cell carcinoma in whom distant metastases were initially radioiodine negative or only weakly positive. Redifferentiation therapy with 13-cis retinoic acid induced a significant radioiodine uptake in metastatic tissue. Thyroglobulin (Tg) immunostaining and autoradiography of a bone metastasis in the right femur, which was initially radioiodine negative, proved Tg synthesis, combined with iodine incorporation into tumor cells. Glucose metabolism in metastases was partially increased and partially unchanged after redifferentiation therapy. The distinct increase of serum Tg after retinoic acid treatment was interpreted as a functional sign of redifferentiation.

rCBF SPECT and the acetazolamide test in the evaluation of dementia

BACKGROUND

The diagnostic potential of 99mTc-HMPAO following systemic administration of the cerebral vasodilator acetazolamide (acetazolamide test) was evaluated using regional-cerebral-blood-flow (rCBF) SPECT in patients with Alzheimer's disease (AD) or with vascular-type of dementia (VD).

METHODS

An initial, high-resolution SPELT study was performed with 99mTc-HMPAO, and after 2 days patients were re-evaluated with 99mTc-HMPAO following systemic administration of acetazolamide. Reconstructed SPELT slices were evaluated visually and semiquantitatively by a semiautomatic rCBF map method.

RESULTS

Using 99mTc-HMPAO alone, a bilateral hypoperfusion was found in the temporal and/or parietal regions in 33% (6/18) of VD patients and in 70% (23/33) of AD patients. The vascular reserve capacity, as determined with the acetazolamide test, was not impaired in 22% of the VD patients but in 76% of the AD patients. The differences in the perfusion patterns between VD and AD patients were statistically different (p < 0.01, Fischer's exact test). Of the 6 VD patients with hypoperfusion (bilateral temporal and/or parietal), 4 had a decreased vascular reserve capacity as determined in the acetazolamide test. Decreased reserve capacity was found in only 4 out of 25 patients with AD.

CONCLUSIONS

The acetazolamide test is helpful in rCBF SPECT to differentiate VD from AD.

Pregnancy after ovarian stimulation and intrauterine insemination in a woman with cavernous macrohemangioma of the liver. A case report

BACKGROUND

There are only a few reports on cavernous hepatic hemangiomas after hormonal substitution or during pregnancy. So far, there have been no publications on ovulation stimulation in such patients.

CASE

We report on a 31-year-old, asymptomatic, healthy woman with an incidental ultrasound finding of a cavernous macrohemangioma (diameter, 14 cm) of the liver. For treatment of primary infertility, clomiphene citrate therapy had been administered repeatedly in the past. Because these treatments were not successful and andrologic subfertility existed, homologous intrauterine insemination was recommended. The first treatment cycle with clomiphene citrate, human chorionic gonadotropin and subsequent intrauterine insemination was successful. During pregnancy, 2.5-cm growth of the liver hemangioma and a smaller, second lesion occurred but remained asymptomatic. Primary cesarean section was performed at 37 weeks' gestation to prevent rupture or hemorrhage of the hepatic hemangioma. Macrohemangiomas of the liver are associated with the risk of rupture and severe hemorrhage due to pressure during pregnancy and delivery.

CONCLUSION

During ovulation stimulation, pregnancy and the immediately postpartum period, there was no change in this benign tumor.

[Incidence of lesions described by magnetic resonance imaging in the clarification of focal epilepsy of frontal and temporal origin]

AIM

Today, MRI is an integral part of the presurgical evaluation of patients suffering from partial epilepsy. These patients frequently show focal morphological abnormalities with potential epileptogenic character and surgical resection of these lesions is associated with superior postsurgical outcome as to seizure frequency. Apart from easily detectable defects, such as post-traumatic lesions or cerebral infarction, as wide variety of mainly small abnormalities can be detected using MRI.

METHODS

In this study, 484 patients suffering from partial epilepsy of temporal or frontal onset were evaluated for the incidence of different lesions in this population.

RESULTS

All lesions found were included without evaluating their potential epileptogenicity, which remains to be proven using other procedures (EEG, SPECT, PET, etc.). Involvement of the hippocampal formation was a major finding in temporal lobe epilepsy, which could be detected as sclerosis (T2w-images), atrophy (T2w-TSE or T1w-IR-images) or both (15%). In addition and in declining frequency various tumors (14%), post-traumatic lesion (-5%), and focal cortical dysplasia or other disturbances of cortical integrity (-4%) were found. These lesions are detectable with best contrast on different sequences. As a consequence it is suggested to acquire sequences in 3 dimensions including a T1w-SE, two (coronal and axial) double-echo-SE sequences and similarly two T1w-IR-sequences. The application of contrast media can be restricted to special questions, derived either from the first imaging results or from the patients history.

CONCLUSION

Using qualitative data for interpretation, the sensitivity as to the detection of any focal pathology of a recent-generation MRI in this population was 75%, with 79% for temporal lobe epilepsies and 67% for frontal lobe epilepsies. Quantitative measurements of hippocampal volume or signal seem to be able to increase the sensitivity of the method.

Comparison of 18FDG-PET with 131iodine and 99mTc-sestamibi scintigraphy in differentiated thyroid cancer

18Fluorine-fluorodeoxyglucose (FDG) positron-emission tomography (PET) has emerged as a useful method in various fields of oncology. The aim of the present study was to evaluate the clinical significance of this technique in differentiated thyroid carcinoma and to compare the results with other imaging modalities, particularly with whole-body 131iodine scintigraphy (WBS) and hexakis (2-methoxyisobutylisonitrile) (99m)technetium (I) scintigraphy (MIBI). Whole-body PET imaging using FDG was performed in 54 patients. There were 39 patients with papillary tumors and 15 patients with follicular tumors (including 3 Hürthle-cell carcinomas). Primary tumor stage (pT) was pT1 in 5 cases, pT2 in 19 cases, pT3 in 2 cases, pT4 in 24 cases, and unknown in 4 cases, respectively. Finally, for each case an overall clinical evaluation was done including histology, cytology, thyroglobulin level, sonography, computed tomography, magnetic resonance imaging, and subsequent clinical course, to allow a comparison with functional imaging results. Compared with WBS, FDG-PET gave different results in the majority of cases with recurrence/metastases (11 FDG-true-positive/WBS-negative tumor sites and 8 WBS-true-positive/FDG-negative tumor sites). In 7 patients with recurrence/metastases, FDG-PET and WBS gave corresponding results (10 sites). In 28 patients, FDG-PET and WBS were normal (including 2 false-negative cases). MIBI was performed in 44 cases. FDG-PET was better correlated to MIBI (congruent positive results in 13 tumor sites) than to WBS. Compared with MIBI, FDG-PET was superior in 5 cases (including 3 patients with distant metastases). Two FDG-negative/MIBI-positive tumors were observed. Different tracer uptake mechanisms have to be considered regarding "nonspecific" tumor imaging with FDG-PET or MIBI. Nevertheless, since spatial resolution with respect to tomographic imaging is inferior with single photon emission computer tomography (SPECT) using MIBI, the observed higher sensitivity of PET might be due to the higher spatial resolution of this method. As far as grading could be obtained, FDG-PET seemed to be more sensitive than WBS in high-grade tumors, whereas WBS was positive predominantly in low-grade carcinomas, although statistical significance could not be reached. The results prove the clinical usefulness of FDG-PET and MIBI for detection of 131iodine-negative tumor tissue in differentiated thyroid cancer.

Inzidenz kernspintomographisch erfaßbarer Läsionen bei der Abklärung fokaler Epilepsien frontalen und temporalen Ursprunges

Ziel: Die MRT ist integraler Bestandteil der prächirurgischen Diagnostik von Patienten mit fokalem Anfallsleiden. Diese weisen häufig eine um’schriebene morphologische Läsion mit potentiell epileptogenem Cha’rakter auf, deren Resektion in bis zu 90% der Patienten zu einer deutli’chen oder kompletten Reduktion der Anfälle führt. Neben relativ einfach nachweisbaren Schädigungen, wie z. B. kortikalen Defekten (z. B. Trauma, Infarkt), kommt eine Vielzahl oft winziger Läsionen unterschiedlicher Ätiologie als auslösende Ursache in Frage. Dies stellt eine suffiziente Bildgebung mit der MRT insofern vor Probleme, als auf Grund der untersuchungstechnischen Belastung der Patienten nur eine limitierte Anzahl von Sequenzen durchgeführt werden kann.

Methode: Es wurden insgesamt 484 Patienten mit fokalem Anfallslei’den frontalen oder temporalen Ursprunges hinsichtlich der MR-tomo-graphisch erhobenen Befunde untersucht. Dabei wurde keine Einteilung hinsichtlich einer möglichen Epileptogenität solcher Läsionen vorge’nommen, da diese ohnehin rein morphologisch nicht eindeutig zu be’stimmen ist.

Ergebnisse: In diesem Patientengut konnte gezeigt werden, daß hoch’frequent nachgewiesene Läsionen bei Temporallappenepilepsie in Schä’digungen des Hippokampus (Atrophie, Sklerose) (15%) und darüber hin’aus im Gesamtkollektiv mit absteigender Häufigkeit verschiedene Tu’moren (ca. 14%), Schädel-Hirn-Traumata (ca. 5%), kortikale Anla’gestörungen (ca. 4%) und eine Vielzahl ähnlich häufiger anderer Läsio’nen ursächlich in Frage kommen. Diese Läsionen werden mit jeweils unterschiedlichen Sequenzen sensitiv erfaßt, so daß insgesamt bei fokalen Epilepsien standardisiert 3 Ebenen unter Einschluß einer T1-ge-wichteten-SE-, und von möglichst je 2 (koronal und axial) Doppel-Echo-SE- und T1-gewichteten IR-Sequenzen untersucht werden sollten. Da’gegen ist eine standardisiert durchgeführte Kontrastmittelapplikation nicht erforderlich.

Schlußfolgerung: Die Sensitivität moderner MR-Tomographen liegt bei rein qualitativer Befundung und unter Einschluß sämtlicher umschriebe’ner Pathologien derzeit insgesamt im Bereich von 75% aller Fälle, bzw. bei 79% für temporale und etwa 67% für frontale fokale Epilepsien. Quantitative Volumenbestimmungen und eine T2-Relaxometrie der Hip-pokampi sollen insbesondere bei Temporallappenepilepsie die Sensiti’vität der Methode zu steigern.

Prognostic value of thyroglobulin after thyroidectomy before ablative radioiodine therapy in thyroid cancer

Serum thyroglobulin (Tg) is a suitable marker for differentiated thyroid carcinoma after total thyroid ablation by surgery and 131I therapy. Before the first 131I treatment, Tg is not a reliable tumor marker since it can also originate from remnant tissue. It was hypothesized that the ratio of serum Tg to 131I uptake in the thyroid bed could be used to correct Tg values for variations in remnant tissue.

METHODS

The hypothesis was evaluated in 111 patients with differentiated thyroid cancer (38 follicular/73 papillary). Tg and 131I uptake in the thyroid bed were measured before the first 131I therapy. The ratio of Tg to 131I uptake was determined in four groups: Group A, tumor free (n = 81); Group B, lymph node metastases (n = 11); Group C, distant metastases (n = 11); Group D, later recurrence [during a mean follow-up of 56 mo; (n = 8)]. Wilcoxon two-sample test was performed to determine statistical significance between Group A and Groups B-D.

RESULTS

Significant differences in the Tg/131I uptake ratios (median) between Group A (1.0 ng/ml/%) and Groups B (3.3 ng/ml/%) and D (3.3 ng/ml/%) were observed (p < 0.01). In tumor-free patients (Group A), there was no value higher than 5.7 ng/ml/%. Therefore, a higher ratio, observed in 14 of the 30 remaining patients, was indicative of metastases or later recurrence.

CONCLUSION

The ratio of serum Tg to 131I uptake in the thyroid bed might be used as a prognostic marker for thyroid cancer before implementing ablation with 131I.

"High-dose" radioiodine therapy in advanced differentiated thyroid carcinoma

There is yet no consensus concerning the appropriate regimen of the application of [131I]sodium iodine (Nal) activities to patients suffering from advanced differentiated thyroid carcinoma. We report on a total of 167 applications of [131I]Nal, including 78 applications of 11.1 GBq. Response to high-activity radioiodine therapy (RIT) is correlated to the course of the disease as well as to the reaction of thyreoglobulin and acute/subacute side effects of radiation.

METHODS

Following radioablation of thyroid remnants using 1.85 to 3.7 GBq[131I]Nal, 26 patients with advanced differentiated thyroid carcinoma (follicular, 11; papillary, 4;mixed-cell thyroid carcinoma, 11) were treated with repeated activities of 11.1 GBq[131I]Nal. Initial tumor staging according to UICC showed T4 in 54%, T3 in 19%, T2 in 19% and was not obtained in 8%. Differentiated thyroid carcinoma was multifocal in 23% of patients. Applied accumulated activities ranged from 14.8 to 99.9 GBq with a mean of 55.5 GBq per patient.

RESULTS

Mean post-diagnostical follow-up was 73 mo, mean follow-up after diagnosis of metastatic spread was 48 mo. Follicular thyroid carcinoma remained as stable disease in 7 of 11 patients, 6 of whom showed metastatic disease after a mean of 20 mo, and only 1 complete remission was achieved using high-dose therapies, with progressive disease in the remaining patients. Overall, 73% of follicular thyroid carcinoma had progressive disease without major response to high-activity RIT. In contrast, only 20% of papillary thyroid carcinoma/mixed-cell thyroid carcinoma showed progressive disease, and complete remission was achieved in 47% of patients. Pulmonary and lymph node metastases in the majority of patients showed good response to therapy, whereas local recurrences and bone metastases showed minor reactions to RIT. After low-activity therapies 8% of patients showed WHO grade I hematotoxic reactions. After high-activity therapies, 38% of patients had WHO I, 8% WHO II and one patient had WHO III toxicity (4%).

CONCLUSION

Use repetitive high-activity RIT with a maximum of 44.4 GBq applied during 1 yr and a maximum of 99.9 GBq accumulated activity resulted in a significant increase of hematotoxicity. However, during the follow-up period (mean, 4 yr), no clinical symptoms possibly related to low blood counts were seen in patients with advanced differentiated thyroid carcinoma. Initiation of high-activity RIT in reaction to metastatic tumor outspread to achieve complete remission was found to be useful in treating papillary thyroid carcinoma and mixed-cell thyroid carcinoma, but only in a minority of follicular thyroid carcinoma patients.

Interventional brain SPECT--a review

Brain SPECT with HMPAO or ECD has-due to its short accumulation period--a rather high time resolution of approx 60 sec. Compared to isopropyl amphetamine (I-123) and FDG-PET, shortlasting interventions may be evaluated by SPECT. Usually, a two-step approach is used, injecting one third of the dose under baseline conditions and two thirds during intervention. The first study is then subtracted from the second study, resulting in a "difference" image which allows to calculate the effect of the intervention. These interventional procedures may include drug, mechanical, and mental intervention as well as ictal, blood pressure and receptor intervention. Moreover, the difference of pCO2 after hyperventilation or hypoventilation may also be used as a stimulus. The above mentioned procedures are described in detail.

Evaluation of technetium-99m-ECD in childhood epilepsy

In childhood epilepsy, it is difficult, but of critical importance, to determine whether surgical intervention might be beneficial for an individual patient. Because both established procedures-MRI and electroencephalography (EEG)-have limitations, interictal and ictal regional cerebral blood flow (rCBF) SPECT has proven to be a valuable adjunctive method in the presurgical evaluation of children.

METHODS

We evaluated the usefulness of the new rCBF tracer 99mTc-ECD in 14 children with focal epilepsy (mean age 9.7 yr). Eleven interictal and 8 ictal studies were performed. Results were correlated with ictal and interictal surface EEG, MRI and histological findings and the postsurgical outcome.

RESULTS

On the basis of the presurgical evaluation, nine patients underwent surgery. MRI studies demonstrated pathological features with possible relation to epilepsy in 50%. Overall, interictal 99mTc-ECD SPECT showed areas of hypoperfusion in 80% of patients. Ictal rCBF SPECT was informative in all patients, including one who showed bifrontal hyperperfusion in accordance with EEG results.

CONCLUSION

Technetium-99m-ECD has proven to be of value for interictal and ictal rCBF SPECT in childhood epilepsy. No side effects during or after tracer administration were noticed. Ictal and interictal rCBF SPECT showed good correlation with MRI and EEG results in patients in whom correlation with the postoperative situation was possible and presented additional significant information in those patients with normal MRI and uninterpretable EEG results. No false lateralizations occurred. In children with focal epilepsy, interictal rCBF SPECT may accelerate the application of long-term electrocorticography (ECoG) in patients with normal MRI results. Ictal rCBF SPECT may also help to avoid ECoG, if a focal hyperperfusion correlates with a focal MRI abnormality, and the surface EEG gives no contradictory information.

Quality assurance in breast cancer brachytherapy: geographic miss in the interstitial boost treatment of the tumor bed

PURPOSE

To assess the role of geographic misses in the interstitial boost treatment of breast cancer patients and to evaluate methods of optimizing breast implants in design, performance, and dosimetry.

METHODS AND MATERIALS

During lumpectomy, the tumor excision sites of 89 patients were marked by five hemoclips. Postoperative radiographs demonstrated the clips' positions with respect to the extension of the surgical cavity, which was demarcated by air and hematoseroma. Twenty-seven selected patients received interstitial boosts to the tumor bed. The implant was first designed according to the clinical assumptions of the tumor bed's topography and then compared with the radiological findings. Prior to brachytherapy, the planning of the implant's dimension and the needle guidance was performed under simulator control. Dose distributions were first calculated following the Paris System and then electively optimized for the target volume by changing source positions and dwell times.

RESULTS

Compared to clinical estimations, the radiological determination of the tumor bed's location revealed an overall potential of topographic errors of 51.8% (14 out of 27 patients), rising up to 78.5% in patients with large adipose breasts (11 out of 13 patients). This observation was due to a high mobility of the tissue, leading to varying tumor site projections at the time of mammography, surgery, and brachytherapy. In all patients, the presimulation of the implant resulted in an adequate coverage of the target volume. In 17 of the 27 treated patients, dose distributions were modified to achieve a higher dose delivery in zones where a higher residual tumor load was expected (boost-in-boost).

CONCLUSION

Breast implants have a high potential of geographic misses that can be avoided by intraoperative clip demarcation. The delineation of the tumor bed allows for dose reports actually referring to the target volume and not to the implant system to be obtained. In addition, modern afterloading techniques offer possibilities of individual dose planning with regard to high risk subvolumes within the implanted tissue.

Fluorine-18 fluorodeoxyglucose positron emission tomography in the follow-up of differentiated thyroid cancer

Whole-body fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging was performed during the follow-up of 33 patients suffering from differentiated thyroid cancer. Among them there were 26 patients with papillary and seven with follicular tumours. Primary tumour stage (pT) was pT1 in six cases, pT2 in eight cases, pT3 in three cases and pT4 in 14 cases. FDG PET was normal in 18 patients. In three patients a slightly increased metabolism was observed in the thyroid bed, assumed to be related to remnant tissue. In one case local recurrence, in ten cases lymph node metastases (one false-positive, caused by sarcoidosis) and in three cases distant metastases were found with FDG PET. In comparison with whole-body scintigraphy using iodine-131 (WBS) there were a lot of discrepancies in imaging results. Whereas three patients had distant metastases (proven with 131I) and a negative FDG PET, in four cases 131I-negative lymph node metastases were detectable with PET. Even in the patients with concordant "staging", differences between 131I and FDG were observed as to the exact lesion localization. Therefore, a coexistence of 131I-positive/FDG-negative, 131I-negative/FDG-positive and 131I-positive/FDG-positive malignant tissue can be assumed in these patients. A higher correlation of FDG PET was observed with hexakis (2-methoxyisobutylisonitrile) technetium-99m (I) (MIBI) scintigraphy (performed in 20 cases) than with WBS. In highly differentiated tumours 131I scintigraphy had a high sensitivity, whereas in poorly differentiated carcinomas FDG PET was superior. The clinical use of FDG PET can be recommended in all cases of suspected or proven recurrence and/or metastases of differentiated thyroid cancer and is particularly useful in cases with elevated serum thyroglobulin levels and negative WBS.

[123I]IBZM SPECT for imaging of striatal D2 dopamine receptors in 56 schizophrenic patients taking various neuroleptics

OBJECTIVE

The purpose of this study was to compare the binding of various typical and atypical neuroleptics to striatal D2 dopamine receptors in schizophrenic patients.

METHOD

Fifty-six inpatients with schizophrenia, including 14 with schizoaffective disorder and one with schizophreniform disorder, were evaluated. Fourteen patients were neuroleptic free. Single photon emission computed tomography (SPECT) was performed 90 minutes after intravenous injection of [123I]benzamide ([123I]IBZM). Subsequent semiquantitative analysis of D2 receptor binding was done with the use of the basal ganglia (striatum)/frontal cortex (BG/FC) ratio of activity. Clinical symptoms were rated with the Positive and Negative Syndrome Scale and the Hamilton Depression Rating Scale.

RESULTS

The BG/FC ratios in patients taking typical neuroleptics were significantly lower than those in the neuroleptic-free subjects but not lower than those in the patients taking atypical neuroleptics (clozapine, remoxipride). For atypical antipsychotics, a dose-dependent relationship with striatal D2 receptor binding could not be demonstrated. BG/FC ratios were not significantly correlated with clinical symptoms or with duration of illness.

CONCLUSIONS

The results indicate that [123I]IBZM SPECT is useful for semiquantitative imaging of striatal D2 dopamine receptors and for estimating their blockade by neuroleptics. Thus, it may improve drug monitoring in psychiatric patients. Furthermore, the findings suggest a complex relationship between the antipsychotic effect of atypical neuroleptics and D2 receptor blockade.

18F-fluorodeoxyglucose-PET and 99mTc-bicisate-SPECT in Creutzfeldt-Jakob disease

In a patient with the occipitoparietal form of Creutzfeldt-Jakob disease (CJD) (Heidenhain type) positron emission tomography (PET) demonstrated decreased glucose utilization in the occipital lobes and adjacent cortical regions. Single photon emission computed tomography (SPECT) with 99mTc-bicisate showed a "coupled" decrease in blood flow in identical cortical areas in this patient. In contrast, magnetic resonance imaging (MRI) was normal. In the early stage of CJD, when still no major morphological abnormalities can be observed, functional imaging is useful for differential diagnosis, particularly to exclude other causes of dementia or pathological EEG patterns.

The relevance of interictal rCBF brain SPECT in temporal lobe epilepsy: diagnostical value and effects of spatial resolution

Interictal rCBF-SPECT is frequently being used as an adjunctive method for localization of an epileptogenic area during presurgical evaluation of patients suffering from medically refractory temporal lobe epilepsy. This study retrospectively evaluates interictal rCBF-SPECT using Tc-99m-HMPAO in comparison to the results of MRI. The final results of surface EEG and ECoG and the postsurgical clinical results as to seizure frequency were used a a 'gold-standard' for the evaluation of both imaging procedures. As spatial resolution is discussed to be the major reason for higher sensitivity of F-18-DG-PET compared to rCBF-SPECT, special attention has been paid to the spatial resolution of the different SPECT systems being used in this study. In 55 patients the complete data set could be obtained retrospectively, 36 of them being evaluated using SPECT systems with relatively low spatial resolution (Picker Dyna 2000, Elscint Helix) and 19 pt. being evaluated using moderate- to high-resolution SPECT systems (ADAC Genesys, DSI Ceraspect). Overall sensitivity of the interictal rCBF-SPECT was 75%, with 69% for low-resolution systems and 84% for high-resolution systems. Approximately at the same time when our institution installed the ADAC Genesys, the MRI equipment was changed form the 1.5 T Philips Gyroscan S15 to the 1.5 T Philips Gyroscan ACS II, the latter allowing superior imaging opportunities. Overall sensitivity of MRI was 60%, with 56%, for the Gyroscan S15 and 68% for the Gyroscan ACS II. The overall positive predictive value (PPV) was 87% for the interictal rCBF-SPECT and 87% for the MRI. Due to the lack of true negative studies in this population specificity was not calculated. False lateralization using rCBF-SPECT occurred in 5 pts. (9%), however, in 3 pts. the area of hypoperfusion correlated with a detectable MRI pathology, yet EEG/ECoG revealed the epileptogenic focus to be elsewhere. In conclusion, the interictal rCBF-SPECT revealed reasonable sensitivity and PPV in pt. suffering from focal temporal lobe epilepsy and modern SPECT systems showed significantly improved results. Since there is a variety of possible reasons for regional cortical hypoperfusion, the interictal SPECT could add significant information prior to the application of ECoG. This specially appeared to be useful in patients with abnormal MRI scan. Furthermore, in patients presenting with a clear pathology on MRI and a corresponding EEG focus, ECoG could be avoided if the interictal rCBF-SPECT additionally showed localized and singular involvement of the affected temporal lobe. ECoG was mainly applied in those patients with relatively wide-spread hypoperfusion additionally involving frontal or parietal cortical areas.

[Scintigraphy of the parathyroid glands with 99mTc-MIBI]

AIM

Since about 3 years 99mTc-MIBI is used instead of 201Tl/99mTc subtraction scintigraphy for the localization of parathyroid involvement in hyperparathyroidism (HPT). The sensitivity of the new method was evaluated.

PATIENTS AND METHODS

24 patients aged between 28 and 83 years with surgically confirmed primary HPT were studied. Planar images were acquired 15 minutes and 3 hours after tracer injection. Additionally, in 9 patients dynamic images were obtained for 2 hours to study tracer kinetics.

RESULTS

19 out of 24 adenomas (79%) were identified correctly with 99mTc-MIBI.

CONCLUSION

The sensitivity of the scintigraphy using 99mTc-MIBI is in the range of the 201Tl/99mTc subtraction scintigraphy. Because of the superior logistic and the lower radiation exposure, 99mTc-MIBI can replace the 201Tl/99mTc scintigraphy in the preoperative diagnostic assessment.

Increased technetium-99m-HMPAO uptake in grade II astrocytoma

Most brain tumors show decreased uptake of blood flow tracers in brain SPECT imaging and in some cases meningiomas show increased uptake, mainly associated with high regional blood flow values. A reason for regionally increased tracer uptake is partial epilepsy when a tracer is injected during the ictal phase. We present a case of a histologically proven Grade II astrocytoma in the mesial part of the left temporal lobe that caused complex partial seizures. After tracer injection during a phase without signs of clinical seizure, markedly increased uptake of 99mTc-hexamethylpropyleneamine oxime (99mTc-HMPAO) occurred, although the tumor was partially calcified.

Vascularisation of ocular coralline hydroxyapatite implants

Vascularisation of coralline hydroxyapatite used to replace the enucleated bulb is of critical importance for the uncomplicated implantation of a motility peg connecting the implant with the cosmetic prosthesis. Technetium-99m diphosphopropanedicarboxylic acid (DPD) single-photon emission tomography (SPET) was used to evaluate the rate of vascularisation as well as the time required for completion of vascularisation. Twenty-four patients were enrolled in the study, which was designed to evaluate vascularisation 10 days, 2 months and 4 months after implantation of a coralline implant. Nineteen patients completed the study and the visual impression of the completion of the vascularisation was scored from 0 (no vascularisation) to + (complete vascularisation) for each patient. No tracer accumulation was detected in any patient at the 10-day examination. Increasing vascularisation was demonstrated with time, and full vascularisation of the coralline implant was seen in all but one case by 4 months after implantation. We conclude that vascularisation of ocular coralline hydroxyapatite implants occurs early and is completed by 4 months after implantation in most cases, but should be confirmed at this time by 99mTc-DPD SPET.

Ictal and interictal brain SPECT imaging in epilepsy using technetium-99m-ECD

The aim of this study was to evaluate the use of 99mTc-ethyl cysteinate dimer (ECD), also known as 99mTc-bicisate, in the presurgical evaluation of patients suffering from medically intractable epilepsy.

METHODS

Twenty-three brain SPECT studies (8 ictally and 15 interictally) were performed on 16 patients with a high-resolution annular SPECT system (CERASPECT). For the ictal studies, the tracer was injected in the very early phase of the seizure. The delay between seizure onset and 99mTc-ECD injection was 2-20 sec.

RESULTS

Interictally, all patients showed circumscribed hypoperfusions. In four patients, the SPECT lesion represented only structural defects. Circumscribed increased tracer uptake was observed in all ictal studies. For all patients with temporal lobe epilepsy without significant mass lesion, in whom an interictal and ictal 99mTc-ECD-SPECT study could be obtained, the asymmetry index was 0.88 +/- 0.03 for the interictal and 1.23 +/- 0.08 for the ictal studies.

CONCLUSION

The data suggest that 99mTc-ECD is an effective marker of cerebral perfusion imaging in epilepsy. In comparison to other tracers, it has a high in vitro stability and is therefore particularly useful for ictal studies in the very early phase after seizure onset.

Evaluation of cerebral vasoreactivity by SPECT and transcranial Doppler sonography using the acetazolamide test

rCBF SPECT with 99mTc-HMPAO was performed prospectively in 29 patients (3 controls and 26 stroke patients) as well as TCD studies in 20 patients (3 controls and 17 stroke patients) before and after 1 g i.v. acetazolamide. The sensitivity of rCBF SPECT increased from 62% to 77% after acetazolamide provocation in stroke patients. In patients with a reversible neurological deficit, the sensitivity under resting conditions was 50% which increased to 71%, while in cases with a permanent deficit it increased from 75% to 83%. In the evaluation of the cerebrovascular reserve capacity the results of rCBF SPECT and TCD coincided in 91% of the hemispheres. The correlation was statistically significant.

Brain single-photon emission tomography using technetium-99m bicisate (ECD) in a case of complex partial seizure

The clinical application of technetium-99m bicisate (ethyl cysteinate dimer, ECD) for ictal and interictal studies of regional cerebral blood flow (rCBF) in a patient suffering from medically intractable simple and complex partial seizures is reported. The interictal study was performed 60 min p.i. and the ictal studies were performed at 60 min p.i. using an annular crystal single photon emission tomography (SPET) system dedicated for high-resolution brain SPET imaging. Visual evaluation of the studies was carried out, as well as semiquantitative measurement of regional tracer uptake. Magnetic resonance imaging (MRI) scans revealed atrophy of almost the complete left frontal lobe and the ventral parts of the left temporal lobe, including in part the temporomesial structures. The left parietal and occipital structures and the right hemisphere were normal. The interictal study showed a large perfusion defect involving the whole left frontal lobe as well as the left temporal lobe with remaining small areas of normal cortical tracer uptake. The ictal studies detected circumscribed hyperperfusion within the left mesial temporal lobe (ventral part of the hippocampus). Additionally an increase in perfusion could be seen within the entire remaining left temporal lobe. Semiquantitative evaluation of tracer uptake comparing both studies detected markedly increased uptake within the focus compared to the remaining left temporal lobe. On this basis the newly available tracer for studies of rCBF, 99mTc-bicisate, seems to be of value for the detection of epileptogenic foci. Additionally, the value of ictal rCBF studies in the presurgical evaluation of those patients presenting severe morphological alterations on MRI is clearly underlined by this case.

[Changes in the blood picture after radioiodine therapy of thyroid cancer]

AIM

In this study the effect of radioiodine which was administered because of thyroid carcinoma on blood count and various other parameters was examined.

PATIENTS AND METHODS

In 567 patients who had been treated because of a thyroid carcinoma between 1980 and 1990 with radioiodine, changes of hemoglobin, RBC, WBC, platelets, potassium, uric acid, gamma GT, GOT, GPT and AP were measured in correlation with the totally administered dose.

RESULT

In low doses (< 18.5 GBq [500 mCi]), which are sufficient in most cases with clinical course without complications, relevant changes of blood count (hemoglobin: < or = 9.0/10.5 g/dl, RBC: < or = 3.1/3.5 10(12)/l (female/male), WBC: < or = 2.5 10(9)/l, platelets: < or = 0.5 10(11)/l) were observed in only 5 out of 469 cases. After moderate doses (> or = 18.5 GBq [500 mCi] and < 37 GBq [1000 mCi]) we found in only 1 out of 77 cases relevant changes. After very high doses (> or = 37 GBq [1000 mCi]), which are used to treat metastases and/or recurrences, thrombopoesis is most sensitive to the radiation exposure of the bone marrow. Relevant decrease of RBC and WBC were observed in 2 out of 21 patients. Pancytopenia (hemoglobin: < or = 12.0/13.5 g/dl, RBC: < or = 3.9/4.3 10(12)/l [female/male], WBC: < or = 3.5 10(9)/l, platelets: < or = 1.4 10(11)/l) occurred in 4 cases.

CONCLUSION

In high-dose therapy with radioiodine frequent (monthly, but in any cases before each therapy) controls of blood count are necessary. In patients without metastases or recurrence no relevant changes can be expected in most cases.

Disseminated bone marrow metastases from primary breast cancer: detection and follow-up by radioimmune bone marrow scintigraphy

Bone scintigraphy of a 40-yr-old patient suffering from primary breast cancer suggested the possibility of diffuse metastases. Bone marrow scintigraphy using 99mTc-labeled monoclonal antibodies (BW 250/183) demonstrated diffuse destruction of bone marrow due to metastatic disease and consecutive bone marrow extension. Bone marrow scintigraphy was highly sensitive in detecting progression of disease in this asymptomatic patient.

[Orbital implants of coralline hydroxyapatite as eye replacement after enucleation]

BACKGROUND During the last two decades, hydroxyapatite has become popular as alloplastic material for bone replacement in orthopedic and dental surgery. We investigated prospectively the feasibility of hydroxyapatite spheres as replacement of enucleated eyes. PATIENTS AND METHODS Thirty-three consecutive patients entered a prospective study designed to evaluate the results obtained after either primary (n = 26) or secondary (n = 7) implantation of a hydroxyapatite sphere as replacement of the enucleated eyeball. Each patient was examined preoperatively, 1, 2, and 4 months after surgery, as well as every 6 months thereafter. At each examination time the motility of both coralline sphere and overlying cosmetic prosthesis was evaluated and the conjunctival sac was carefully examined at the slit-lamp. RESULTS The postoperative follow-up averaged 10.5 months for the primary implantations and 7.2 months for the secondary implantations. Two implants had to be removed because of infection unresponsive to antibiotic treatment. Defects in the conjunctiva overlying the implant necessitated wound revision in two cases. A buccal mucosal graft was performed in two additional ones. A temporary cosmetic prosthesis could be fitted in all but two of the remaining patients as early as 3 weeks after surgery. Motility of at least 3 mm in all directions could be obtained in 31 cases. CONCLUSION Our study demonstrated that satisfactory motility and good biocompatibility can be achieved, at least in the medium term, with implantation of coralline hydroxyapatite spheres.

Cerebral blood flow in Sneddon syndrome

Sneddon syndrome is defined as a clinical entity consisting of livedo racemosa generalisata (LRG) and cerebrovascular lesions, which often lead to physical and mental handicaps. Four patients with LRG and the suspected diagnosis of Sneddon syndrome had HMPAO-SPECT studies. The patients underwent CT and/or MR brain imaging and three patients had Duplex sonography of the cerebral arteries (TCD). Brain SPECT was abnormal in all patients, whereas CT/MRI revealed a cerebral lesion in only one patient and all TCD studies were normal. HMPAO-SPECT is valuable in detecting disturbed regional cerebral blood flow before irreversible ischemic insults occur, thus allowing the diagnosis of Sneddon syndrome at an early stage.

[99mTc-MAA enrichment in the liver during a cavo-portal shunt over a recanalized umbilical vein]

Lung perfusion scintigraphy in a patient suffering from superior vena cava obstruction showed distinct MAA uptake in parts of the liver due to a collateral blood flow through abdominal parietal veins and a recanalized umbilical vein. Radiation therapy of mediastinal lymphomas was followed by a rapid decrease of caval portal shunt volume.

[Brain SPECT with 123I-labelled iodobenzamide (IBZM): aspects of semiquantitative evaluation]

The striatal dopamine-D2-receptor uptake of 123I-IBZM in 32 patients (18 without and 14 under therapy with typical neuroleptics) was measured semiquantitatively using different ROI techniques. The aim of the study was to evaluate the influence of these techniques on the different ratios (striatum/cortex) found by various examiners. Using the same SPECT system no major differences were found between rectangular and manually drawn ROIs of the same size. All ROI techniques could differentiate between patients with and without therapy on a highly significant level. Therefore, the resulting ratio is mainly dependent on the spatial resolution of the camera system and only to a relatively minor extent on the ROI technique. Ratios obtained by different observers are not comparable quantitatively.

[HMPAO-SPECT in Alzheimer-type dementia and major depression with memory disorders]

The aim of the present study was to see whether HMPAO-SPECT may contribute to the differentiation between dementia of the Alzheimer type (DAT) and major depression (MD). The results in 77 patients with memory impairment were evaluated. 48 patients suffered from DAT and 29 from MD. Initially, the defects in SPECT imaging were attributed to a cerebral region and the degree of decrease was evaluated (-1/-2/-3). Thereafter, the results were classified by 7 categories. In some of these categories an accumulation of cases of either DAT or MD was found. 35% of the patients suffering from DAT had bilateral defects with distinct (> -1) parietal/parietotemporal hypoperfusions, but no patient with MD showed this perfusion pattern. 62% of the patients with MD had unilateral defects but only 31% of the patients with DAT. The present study demonstrates that only 35% of all patients suffering from DAT show a perfusion pattern, thought earlier as "pathognomonic" for this disease. This perfusion pattern--if it exists--may be used as a safe criterion to exclude MD. Beyond that no clearcut ("specific") perfusion pattern may be recognized but unilateral defects point to MD.

Hirn-SPECT mit 123J-markiertem Iodobenzamid (IBZM): Aspekte der semiquantitativen Auswertung

Die striatale Dopamin-D2-Rezeptoranreicherung von 123J-IBZM wurde bei 32 Patienten (18 ohne und 14 mit neuroleptischer Therapie) semiquantitativ unter Anwendung verschiedener ROI-Techniken ausgewertet. Ziel der Studie war es, die von verschiedenen Untersuchern gefundenen unterschiedlichen Quotienten (Striatum/Kortex) unter dem Aspekt der angewandten ROI-Technik zu untersuchen. Es konnte gezeigt werden, daß bei Verwendung des gleichen SPECT-Systems keine größeren Unterschiede zwischen Rechteck-ROI und manuell erstellten ROI gleicher Größe auftreten. Eine hochsignifikante Trennung zwischen behandelten und unbehandelten Patienten ergab sich für alle untersuchten Auswerteverfahren. Der ermittelte Quotient wird wesentlich durch das Auflösungsvermögen der Kamera und nur relativ geringfügig durch die verwendete ROI-Technik bestimmt. Die Quotienten verschiedener Arbeitsgruppen sind quantitativ nicht miteinander vergleichbar.

Circulating activated platelets in myeloproliferative disorders

Platelet activation in patients with myeloproliferative disorders is often suggested by increased platelet alpha-granule secretion and an acquired storage pool defect of dense granules. To determine whether activated platelets circulate in patients with chronic myeloproliferative disorders, we evaluated the binding of monoclonal antibodies against activation-dependent epitopes on resting platelets (P 12, CD 63, and CD 62) in 12 patients with prominent megakaryocytic proliferation (8 patients with essential thrombocythemia, 2 with chronic myeloid leukemia, and 2 patients with polycythemia rubra vera). In addition, platelet aggregation in response to collagen, adenosine diphosphate, platelet activating factor, and agglutination with ristocetin was investigated. In 3 patients there was an increased percentage of platelets binding at least 1 activation marker. In 2 other patients, a trend towards increased antibody binding was observed. Binding of the antibody to thrombospondin (P 12) was related to expression of the GMP 140 protein (CD 62, r = 0.76, p = 0.004). There was no correlation of platelet aggregation defects in vitro to increased expression of platelet activation markers or to thrombohaemorrhagic complications. However, circulating activated platelets were detected in three out of five patients with a history of bleeding or thrombotic complications. The results of this preliminary study suggest that some but not all patients with myeloproliferative disorders showed increased amounts of circulating activated platelets. The relation of bleeding and thrombotic complications to the expression of activation-dependent epitopes on platelets in myeloproliferative disorders requires further investigation.