Platelet dysfunction in myeloproliferative syndromes

Osteomyelosclerosis with thalassemia trait: report of a rare association, study of platelet function tests and review of literature

Idiopathic myelofibrosis is a chronic myeloproliferative disorder characterized by excessive connective tissue deposition in the bone marrow. It presents with leucoerythroblastic anemia and massive splenomegaly. It is termed osteomyelosclerosis in the presence of primitive bone formation in the bone marrow and radiological presence of osteosclerosis. A 40-year-old male, known case of thalassemia trait presented with fatigue and lump in the abdomen for two months. Physical examination showed splenomegaly 8.5 cm below costal margin. X-ray examination revealed multiple osteosclerotic lesions involving the pelvis and long bones. Hemogram showed: hemoglobin 7.8 gm/dl, TLC 47,500/mm(3); DLC was polymorphs 49%, lymphocytes 7%, eosinophils 4%, basophils 4%, blasts 5%, promyelocytes 2%, myelocytes 14%, metamyelocytes 10%. Platelet count was 60,000/mm(3). Peripheral blood film showed leucoerythroblastic blood picture with features of dysmyelopoiesis. Bone marrow aspiration was diluted with peripheral blood. Bone marrow biopsy showed replacement of marrow by grade III reticulin fibrosis. Bony trabaculae were wide and thick. Platelet function studies were abnormal. The clinical, radiological and hematological features suggested a diagnosis of osteomyelosclerosis. We present this case because no similar association of osteomyelosclerosis with thalassemia trait has been described in English literature to date. This is the first study from India, which describes platelet function tests in a patient with osteomyelosclerosis.

Hemorrhagic and thrombotic complications in patients with myeloproliferative diseases

OBJECTIVE

To correlate the incidence of hemorrhage and thrombosis to bleeding time (BT) and platelet aggregation in 27 consecutive patients with myeloproliferative diseases (MPD).

DESIGN

Retrospective study.

SETTING

Public tertiary referral center.

PATIENTS

Eighteen patients with chronic myelogenous leukemia (CML), 5 with polycytemia vera (PV), 2 with essential thrombocytemia (ET) and 2 with idiopathic myelofibrosis (MF). Duke's BT and epinephrine-induced platelet aggregation were performed on the patients and on 10 healthy individuals.

RESULTS

Eleven patients presented symptoms (41%):9 with hemorrhage (33%) and 5 with thrombosis (19%). There were less symptomatic patients in the CML group (28%) than in the other MPD (67%), without statistical significance (Fisher, p = 0.06). Duke's BT was longer in symptomatic patients (Mann-Whitney, p < 0.05). Platelet aggregation was abnormal in 7 patients (26%) and 71% of them were symptomatic (Fisher, p = 0.07).

CONCLUSIONS

The high incidence of bleeding and thrombosis in patients with MPD was related to prolonged BT, but not to platelet aggregation abnormalities.

An abnormal pattern of multiple platelet function abnormalities and increased thromboxane generation in patients with primary thrombocytosis and thrombotic complications

Platelet aggregation (PA) induced by ADP, collagen and epinephrine, plasma levels of beta-thromboglobulin (beta TG) and thromboxane B2 (TXB2) and serum TXB2 generation were studied in 11 patients with primary thrombocytosis (7 with essential thrombocythaemia and 4 with polycythaemia vera) and compared with 16 healthy subjects. 5 patients suffered from peripheral vascular ischaemia and another 3 had venous thrombosis, but none had bleeding complications. The patients showed an abnormal pattern of platelet function and of thromboxane generation distinct from the healthy subjects in three aspects. a) Shape change was 5-26 times greater, the lag-time of collagen PA was 2.3-2.9 times longer and the extent of epinephrine PA was nil or very low. ADP- or collagen-induced PA was also reduced (p less than 0.02). b) Plasma TXB2 generation (corrected to a normal platelet concentration) stimulated by the three PA inducers was within the range of the healthy subjects in spite of the reduced extent of PA. c) Plasma beta TG level and serum TXB2 generation (both corrected to a normal platelet concentration) were 2.9-7.1 times higher (p less than 0.001) indicating enhanced in vivo platelet activation and possibly increased thrombin generation. These abnormalities were not detected in another 4 patients with secondary thrombocytosis. The abnormal pattern of platelet function and thromboxane generation can be a useful laboratory method in the evaluation of patients with primary thrombocytosis. It might also explain the thrombotic complications which occurred in 8 of the patients in a manner such that increased or normal TXB2 generation overcomes the reduced extent of PA. In this respect, the pronounced serum TXB2 synthesis might be a marker of intravascular thrombosis.

Platelet function and interferon alpha-2a treatment in essential thrombocythaemia

The effects of interferon (IFN) alpha-2a treatment on platelet function were evaluated in 20 patients affected by essential thrombocythaemia (ET). Baseline data documented the well-known abnormalities of in vitro platelet aggregation and the constant presence of a delta-storage pool deficiency. The therapy in all patients reduced the platelet count, and in the majority of them caused a partial improvement of in vitro platelet aggregation. Although the mean intraplatelet ADP level improved during treatment, it always remained below the normal range documenting persistence of the delta-storage pool deficiency. The plasma beta-TG levels, which initially were high, significantly decreased during treatment, but the beta-TG ratio and the platelet beta-TG values always remained within the normal range--this suggests an absence of platelet activation either before or during therapy. Our results demonstrate that, despite significantly reducing the platelet count, IFN alpha-2a treatment only partially corrects the qualitative platelet abnormalities in ET.

Platelets of patients affected with essential thrombocythemia are abnormal in plasma membrane and adenine nucleotide content

The adenine nucleotides present in distinct cellular compartments of platelets of 27 patients affected with essential thrombocythemia have been measured. In order to quantify granule-bound nucleotides and adenylic cytoplasmic pool, platelets have been stimulated with thrombin or treated with increasing digitonin concentrations, respectively. Among patients, we have identified two groups: 12 patients (Group 1) had normal platelet level of ATP and ADP both in dense granules as well as in cytoplasmic pool. The other patients (Group 2) had granule ATP and ADP significantly lower and ATP/ADP ratio significantly higher than controls. In these patients an increase in hypoxanthine level, derived from metabolic ATP degradation occurring during stimulation, was observed. In addition, in the latter patients an increased resistance of plasma membrane to digitonin was shown, suggesting that membrane fluidity should be reduced owing to a modified cholesterol/phospholipid ratio.

Platelet function in myeloproliferative disorders: characterization and sequential studies show multiple platelet abnormalities, and change with time

Bleeding and thrombosis are well known major causes of morbidity and mortality in patients with myeloproliferative disorders (MPD) but the relationship between these clinical events and the commonly found platelet function abnormalities have not been established. In this study we performed simultaneous laboratory evaluations in 54 patients with MPD to investigate abnormalities in platelet aggregation and cyclooxygenase activity, the latter by using an in vitro aspirin inhibition test; the studies were repeated in 22 patients 1-27 months later. We have found platelet hyper- and hypofunction co-existing in some patients (9/54), and change of platelet function during the course of the disease (7/22) with platelet hypofunction being the only constant abnormality over time. These results may explain the lack of correlation between the clinical events and the limited assessment of platelet function in the hitherto published studies, and also suggest the need for repeated evaluations to properly assess the relative risk for bleeding and thrombosis.

Platelet-associated IgG and IgM in myelofibrosis

Elevated levels of platelet-associated IgG and/or IgM were found in 15 of 18 patients with myelofibrosis (83%). All but 5 patients with elevated PAIg had active disease. The amounts of PAIg were not correlated to either S-Ig, platelet count or spleen size. Levels of PAIgG well above the normal range were especially found in patients with short duration of disease and/or a transitional myeloproliferative state. It is debated whether immune-mediated platelet dysfunction may be of importance for the development of bone marrow fibrosis, mediated by the release of platelet-derived growth factors in the bone marrow. Elevated PAIg may also contribute to abnormal haemostasis and thrombocytopenia in myelofibrosis.

Prognostic factors in myelofibrosis

The prognostic significance of spleen size, hemoglobin level (Hb), platelet count and hemopoietic cellularity of the bone marrow was assessed in 33 patients with myelofibrosis. Of these 4 parameters, only the Hb (P less than 0.01) and bone marrow cellularity (P less than 0.001) were found to be useful indicators of prognosis. Patients with Hb greater than 10 g/dl had a median survival greater than 110 mth while those with Hb less than 10 g/dl had a median survival of 22.5 mth; patients with hemopoietic hypercellularity in the bone marrow had a median survival greater than 110 mth while those with a normo- or hypocellularity had a median survival of 20.5 mth. There was significant correlation (P less than 0.01) between the marrow cellularity and the Hb level; 71% of patients with a normo- or hypocellular marrow had Hb less than 10 g/dl, while 79% of those with a hypercellular marrow had Hb greater than 10 g/dl.