A patient with Crow-Fukase syndrome associated with pulmonary plasmacytoma]

We here reported a 54-year-old female patient with Crow-Fukase syndrome associated with pulmonary plasmacytoma. She was found to have scattered tumor in 1990. Although the tumor had slowly grown for the last 10 years, she showed no clinical symptoms. Numbness and weakness of lower extremities began in June 1999, and she was referred to Kyoto University Hospital on Oct. 21 1999 for evaluation of progressive symptoms. She had skin pigmentation, edema of the lower extremities, lymphadenopathy, muscle weakness and sensory disturbance in a glove-and-stocking distribution. Serological examination showed monoclonal IgG-lambda gammopathy. Serum vascular endothelial growth factor (VEGF) was markedly elevated. Microscopic studies on biopsied sural nerve demonstrated mild decrease of myelinated fibers. Immunohistochemically, the pulmonary tumor was defined as an IgG (lambda type) plasmacytoma. After treatment with melphalan-prednisolone therapy, the neurological symptoms improved along with decrease of serum VEGF levels as well as the size of pulmonary plasmacytoma. This is the first report of a patient with Crow-Fukase syndrome associated with pulmonary plasmacytoma. This case suggests that growth of pulmonary plasmacytoma might have played an important role in the overproduction of VEGF and thus development of Crow-Fukase syndrome.     

A case of Crow-Fukase syndrome associated with idiopathic thrombocytopenic purpura

A 40-year-old man was admitted to our hospital because of paresthesia and weakness of the limbs. At the age of 38, he was diagnosed as having an idiopathic thrombocytopenic purpura (ITP) which have been refractory to oral administration of prednisolone and splenectomy. Platelet-associated IgG was elevated markedly at that time. It was, however, only mildly elevated on this admission. He showed polyneuritis, generalized pigmentation, hirsutism, and marked edema on the legs. The bone X-ray disclosed a lytic lesion in the left iliac bone, which was confirmed as a plasmacytoma by bone biopsy. Axonal degeneration with marked loss of myelinated figure was seen on sural nerve biopsy. Serum immunoelectrophoresis revealed his monoclonal IgG was lambda type. Then, he was diagnosed as having a Crow-Fukase syndrome associated with ITP. Plasma exchange, pulse therapy, and irradiation to plasmacytoma resulted in a slight improvement of the polyneuritis and the skin symptoms, and a disappearance of edema. However, ITP has not responded to these therapies. Although the same autoimmune mechanism is suggested in these conditions, we could not clarify how this monoclonal IgG produce both polyneuritis and ITP.     

Crow-Fukase syndrome associated with Castleman disease showing hypertrophic cranial pachymeningitis and bilateral internal carotid artery occlusion]

A 51-year-old woman was diagnosed as Crow-Fukase syndrome on July 1997, presenting with lymph node swelling, polyneuropathy, hepatomegaly, hypothyroidism, renal dysfunction, edema and skin change. Lymph node swelling and polyneuropathy improved in some degree after chemotherapy. She was admitted to our hospital on march 6, 1998 because of consciousness disturbance, right hemiparesis and non-fluent aphasia after fever and hypotension. The next day of admission, consciousness disturbance, right hemiparesis and non-fluent aphasia disappeared. MR images of the brain revealed low intensity on a T1-weighted image and high intensity on a T2-weighted image in the left parietal lobe. Furthermore, MR images also revealed diffuse hypertrophic dura matter with enhancement by Gd-DTPA, which made the diagnosis of chronic cranial pachymeningitis. The cerebral angiographies showed bilateral internal carotid artery occlusion. The cerebrospinal fluid showed normal cell count, total protein level of 82 mg/dl, and IgG level of 18 mg/dl. Since there has been very few case reports describing intimate relationship between Crow-Fukase syndrome and pachymeningitis, and between carotid occlusion and pachymeningitis, we speculated that the pachymeningitis might be associated with Crow-Fukase syndrome. Furthermore, pachymeningitis might be a cause of her bilateral carotid occlusion. The number of cases of Crow-Fukase syndrome associated with cerebrovascular disease was very rare. This is the first case which had bilateral internal carotid artery occlusion probably caused by chronic cranial pachymeningitis. Therefore, it is necessary to pay attention to cerebrovascular disease when the patient of Crow-Fukase syndrome is associated with pachymeningitis.     

A case of Crow-Fukase syndrome showing improvement following excision and irradiation of bone lesions]

A 57-year-old woman suffering from pleural and pericardial effusion, pulmonary hypertention, lymphadenopathy, hepatosplenomegaly, edema, hypertrichosis, small hemangioma and polyneuropathy was diagnosed as Crow-Fukase syndrome. Osteoctomy of the left second rib and irradiation of this rib and the left iliac bone were performed. Serum vascular endothelial growth factor (VEGF) level decreased to less than one-half the level before the operation (from 5,180 to 2,150 pg/ml). Immediately after the operation, pleural and pericardial effusions due to hyperpenetration improved, and polyneuropathy and hypertrichosis due to hypervasularity also gradually improved. The resected lesion was histopathologically found to be of a plasmacytoma of the IgG lambda type. Since the level of VEGF in the tissue specimen was much lower (116 pg/ml) than that in the serum, VEGF could not have been produced by the plasmacytoma.     

Quantification of platelet-associated IgG for differential diagnosis of patients with thrombocytopenia

Immune thrombocytopenia is due to platelet destruction by circulating glycoprotein-specific antibodies and is found in various disorders. Methods for the detection of platelet-associated IgG (PAIgG) are generally sensitive but unspecific, whereas glycoprotein-specific assays are highly specific but less sensitive. Usefully, a sensitive screening method for PAIgG detection would also provide information for differential diagnosis. We developed a quantitative direct Platelet Immunofluorescence Test (PIFT) by flow cytometry and studied 79 thrombocytopenic patients with immune thrombocytopenia and other disorders. The sensitivity of the assay was 94%, its specificity 66% for the detection of a clinically obvious immune thrombocytopenia. PAIgG levels of patients with immune thrombocytopenia differed significantly from those of other patients with low platelet counts (p <0.001). The quantitative PIFT proved to be a sensitive method for PAIgG detection and should therefore be used as a screening method. In addition, it could be helpful for differential diagnosis in marked thrombocytopenia where a MAIPA is not feasible.     

A case of polyneuropathy associated with increased levels of vascular endotherial growth factor (VEGF) insera]

A 54-year-old woman began to notice numbness and motor weakness in the lower extremities in July 1999. These symptoms rapidly progressed and she could not walk any more. When she admitted to our hospital, she showed peripherally dominant, moderate motor weakness, drop foot and loss of superficial and deep sensation in the lower extremities, but only slight weakness in the hands. Cranial nerves were intact. Deep tendon reflexes were all absent. Nerve conduction velocities were reduced and cerebrospinal fluid protein was elevated. VEGF was greatly increased in serum (1,850 pg/ml), which has been found to be increased exclusively in patients with Crow-Fukase syndrome. Many characteristic manifestations of the syndrome except polyneuropathy are well explained to be resulted from the abnormal production of VEGF. She did not, however, exhibit any constellation of Crow-Fukase syndrome such as edema, skin change, organomegaly, bone lesions or M-proteinemia. Steroid therapy improved her symptoms and lessened the levels of serum VEGF and cerebrospinal fluid protein. This case indicated that overproduction of VEGF could induce polyneuropathy rather than the other symptoms of Crow-Fukase syndrome, and that a polyneuropathy associated with increased VEGF might exist.     

A case of Crow-Fukase syndrome with increased serum interleukin-6]

We experienced a 47-year-old Japanese female with polyneuropathy, edema, hypertrichosis, hyperpigmentation, and white nail, which were diagnostic as having Crow-Fukase syndrome. Laboratory and radiological evaluation showed neither plasma cell dyscrasia nor monoclonal gammopathy. Increased factor VIII activity and thrombocytosis, which suggested thrombotic tendency, were observed at the exacerbation of clinical symptoms. In her third exacerbation, she presented marked cyanosis in her right foot, and angiography confirmed narrowing of arteries at the ankle. Increased serum interleukin-6 was also observed, and the production of interleukin-6 by endothelial cells of cutaneous angioma was shown. Possible role of interleukin-6 in Crow-Fukase syndrome was discussed.     

The role of interleukin-6 in Crow-Fukase syndrome]

We measured serum interleukin-6 (IL-6) levels in 14 patients with Crow-Fukase syndrome. Five out of 14 patients with Crow-Fukase syndrome showed high serum IL-6 levels above 10 pg/ml, which was statistically significant in comparison with control subjects with other neurological diseases. Serial studies of serum IL-6 levels in two patients revealed the increase before the exacerbation of clinical symptoms of edema, and pleural or cardiac effusion, and the fall after the treatment by high dose pulsed methylprednisolone. We suggest that serum IL-6 level appears to be a useful marker to predict its exacerbation. Also we performed immunohistochemical study on cutaneous angioma from three Crow-Fukase syndrome patients using anti-IL-6 antibody. The cytoplasm of endothelial cells of cutaneous angioma from two patients was positively stained, which might imply the abnormality of endothelial cells in Crow-Fukase syndrome.     

A case of Crow-Fukase syndrome with respiratory failure due to bilateral diaphragmatic paralysis]

A 62-year-old man with well-controlled diabetes mellitus developed numbness of the bilateral feet and hands, followed by subacutely progressive weakness and amyotrophy of extremities. He became bed-ridden state, and dyspnea also appeared, so he was referred to our hospital. Physical examination revealed a lean man, with dark-reddish skin pigmentation, crabbed fingers, bilateral pretibial pitting edema, and bristles in extremities. Thoracoabdominal paradoxical respiration was observed and pulmonary vesicular sounds was decreased markedly in the both lungs. Laboratory data revealed hypoproteinemia, abnormalities of endocrine system, but M-protein was not detected. Serum vascular endothelial growth factor level was quite high. Chest radiography revealed elevation of the bilateral diaphragm, the % vital capacity (%VC) was 24%, and arterial blood gas analysis showed marked hypoxia with hypercapnia. These findings suggested that his respiratory failure was induced by bilateral diaphragmatic paralysis caused by bilateral phrenic nerve palsy due to Crow-Fukase syndrome. He became somnolent because of hypercapnic narcosis, so non-invasive positive pressure ventilation (NIPPV) was started. We treated him with intravenous immunoglobulin and oral corticosteroids therapies, and after these therapies, his symptoms were remarkably recovered and NIPPV became unnecessary soon. The most frequent causes of respiratory failure in Crow-Fukase syndrome are pleural effusion and pulmonary hypertension, and only two cases of this syndrome with respiratory failure caused by bilateral diaphragmatic paralysis were reported until now. When the patients with Crow-Fukase syndrome complain of dyspnea, we should take the diaphragmatic paralysis into consideration, which may be improved by appropriate therapies.     

A case of Crow-Fukase syndrome with extramedullary plasmacytoma: marked clinical deterioration following a biopsy to plasmacytoma]

A 66-year-old man developed paresthesia of the distal parts of the bilateral lower limbs a week after his upper respiratory infection, followed by the weakness with the legs and paresthesia with the lip area, tongue and finger tips. Those symptoms gradually became worse to the point that he was unable to walk 10 days later. Although skin pigmentation, edema, and lymph node swelling were not found, we made a diagnosis of Crow-Fukase syndrome (CFS) because of clinical features of polyneuropathy, IgG-lambda type M proteinemia, endocrinological abnormality, elevated plasma level of vascular endothelial growth factor (VEGF) and extramedullary plasmacytoma in his abdomen. Following intravenous immunoglobulin therapy (IVIg), he showed marked improvement. However, his neurologic symptoms deteriorated acutely just after open biopsy together with the elevation of VEGF level, and a few days later he was in the state of flaccid quadriparesis. We tried IVIg therapy again and his neurologic symptoms were markedly improved. We speculated that an elevated VEGF, released from plasma cells induced by the bioprocedure, might have caused an increase in microvascular permeability and affected the blood-nerve-barrier, thereby his neurologic symptoms deteriorated. It is thought that this case may support the hypothesis that a significant role is played by VEGF in the pathomechanism of the development of CFS. Additionally we experienced that IVIg was very effective to the neurologic symptoms, and we think that IVIg will be able to be one of the future therapy of the CFS. To our knowledge, there has been no report of CFS which manifested acute deterioration of his neurologic symptoms just after open biopsy with acute onset with Guillain-Barré syndrome like symptoms.     

Crow-Fukase syndrome

In Japan, Crow-Fukase syndrome is a target of active research because of many cases reported. Therefore, the following three topics regarding this syndrome were discussed. 1) Etiology of Crow-Fukase syndrome. Even in reported cases of Crow-Fukase syndrome with monoclonal protein or polyclonal immunoglobulins and no apparent multiple myeloma, there were plasmacytomas in the lymph node or other tissues, and symptoms became improved after removal of these tumors. Therefore, plasma cells seem to be involved. According to recent studies, impairment of the pituitary function may play some role. 2) New pathological findings in the lymph node histology. In the lymph node of patients with this syndrome, we found in its germinal center a peculiar abnormality called angiosclerosis, in which branching tortuous capillaries with thickened wall including many cells were prominent, which may be different from those of Castleman's disease. 3) Nerve conduction studies using a new collision technique. Crow-Fukase syndrome is associated with marked slowing of even the maximal motor and sensory conduction velocities. Therefore, in order to understand its pathophysiology better, submaximal conduction velocities should be measured using the new collision technique because this technique is different from Hopf's method that is affected by the refractory period of nerve fibers.     

A case of anaphylactoid shock occurring immediately after the initiation of second intravenous administration of high-dose immunoglobulin (IVIg) in a patient with Crow-Fukase syndrome]

We report a case of anaphylactoid shock occurring immediately after the initiation of second intravenous administration of high-dose immunoglobulin (IVIg) in a patient with Crow-Fukase syndrome. The patient was a 57-year-old woman, who was admitted to our hospital because of numbness and muscle weakness in the four extremities, difficulty in walking, and foot edema. On admission, her skin was dry and rough, and also showing scattered pigmentation, small hemangiomas, and hypertrichosis in both legs. She had distal dominant muscle weakness, more prominent in her legs, and was not able to walk. Deep tendon reflexes in her four extremities were markedly diminished or absent. She had a glove and stocking type of paresthesia, severe impairment of vibration, and absence of joint position sensation in her four extremities. On laboratory data, serum vascular endothelial growth factor (VEGF) was markedly elevated to 5,184 pg/ml (normal: below 220 pg/ml). Cerebrospinal fluid examination revealed cell counts of 2/microliter and protein level of 114 mg/dl. Abdominal echo showed marked hepatosplenomegaly. On peripheral nerve conduction study, both motor and sensory conduction velocity were undetectable in her legs. We diagnosed her condition as Crow-Fukase syndrome, and started IVIg of polyethyleneglycol-treated gamma-globulin (PEG-glob) at 400 mg/kg/day for 5 consecutive days for polyneuropathy. Since the first IVIg mildly improved muscle weakness, we tried the second IVIg of PEG-glob. However, immediately after the initiation of second IVIg of PEG-glob, she developed hypotention, dyspnea, cold sweating, cyanosis, and became lethargic. We immediately stopped IVIg and started first-aid treatment with epinephrine and corticosteroid for these symptoms. This treatment was successful and the patient fully recovered without any sequelae. Since serum IgE level remained unchanged and lymphocyte stimulation test (LST) was positive against the same rot number of PEG-glob, we diagnosed these symptoms as anaphylactoid shock. Based on the results of LST, we speculated that PEG-glob was the causative agent of anaphylactoid reaction. Anaphylactic or anaphylactoid reaction as adverse effects of IVIg is very rare, and to our knowledge, there are only 4 previous reports of anaphylactic or anaphylactoid reaction caused by IVIg. Therefore, we speculated that the prominent high level of serum VEGF in the present patient might play a significant contributory role in the development of anaphylactoid shock, since the vascular permeability of VEGF is 50,000 times stronger than that of histamine. We consider that it is necessary to carefully monitor IVIg of PEG-glob administration for polyneuropathy in patients with high level of serum VEGF, like Crow-Fukase syndrome.     

Autoantibody against platelet glycoprotein IIb/IIIa in a patient with non-Hodgkin's lymphoma

An autoantibody to platelet glycoprotein (GP) II b/III a was produced in a 38 year-old woman who had a previous history of the malignant lymphoma of the stomach. The aggregations of the patient's platelets showed losses of the primary waves in response to ADP and epinephrine and marked hypoaggregation in response to collagen, while agglutination by ristocetin was normal. Crossed immuno-electrophoresis (CIE) of her platelets solubilized by 1% Triton X-100 revealed an abnormal biphasic precipitate line of GP II b/III a complex. Nine months later, she developed severe thrombocytopenia along with a relapse of the lymphoma in the cervical lymph nodes. The patient's IgG, which was collected during her thrombocytopenic period and purified, inhibited ADP-, epinephrine- and collagen-induced aggregations of normal platelets. In CIE, the 125I-labelled IgG of the patient, inserted into the intermediate gel, was incorporated into the precipitation line of the GP II b/III a complex of normal platelets. Radiation treatment to the cervical lymph nodes dramatically normalized both the function and the count of the patient's platelets. From these findings, it is suggested that an autoantibody to the GP II b and/or III a was produced by the lymphoma cells.     

Highly concentrated vascular endothelial growth factor in platelets in Crow-Fukase syndrome

We report a marked difference in concentration of vascular endothelial growth factor (VEGF) between serum and plasma in patients with Crow-Fukase syndrome (CFS). The serum/plasma VEGF levels in 4 CFS patients were 8,634/152, 5,203/176, 3,724/127, and 868/13 pg/ml, respectively. We also showed that platelets were a major source of this VEGF and that VEGF was released during platelet aggregation by physiological stimulation. It is suggested that in CFS, local VEGF concentration is markedly elevated by aggregation of platelets containing excessive VEGF and their adhesion to vascular walls, resulting in excessive physiological activities of VEGF. Our findings provide important information for developing more effective therapeutic trials.     

Solitary costal plasmacytoma: a rare cause of subacute demyelinating polyradiculoneuropathy

INTRODUCTION: The solitary plasmacytoma (SP) is a non-frequent, localized variant of multiple myeloma with a single bone lesion and earlier appearance. Polyradiculoneuropathy is the most frequent neurological manifestation. We report the case of a young male who developed a subacute demyelinating polyradiculoneuropathy as the initial symptomatology of a costal SP, which constitutes an extremely infrequent association, given age and site of the lesion. CASE REPORT: A 32-year old, previously healthy, man presented with a one month history of progressive symmetrical paraparesis and paresthesias in feet. The neurological examination revealed 4/5 paraparesis, global arreflexia and hypopalesthesia in legs. Cerebrospinal fluid examination revealed elevated proteins (83 mg/dl) with normal cell count and glucose content. Investigations showed high levels of beta(2)-microglobulin (3 mg/l), and a monoclonal IgG lambda gammapathy. The chest X-ray and thoracic CT revealed an osteolytic lesion in the left third rib. Nerve conduction studies showed sensitive and motor polyneuropathy with secondary axonal degeneration. Bone marrow biopsy was normal. Second and third left ribs were excised, revealing a pathologic diagnosis of plasmacytoma. The patient became asymptomatic after corticosteriod administration lesion excision and local radiotherapy. Conclusions. Subacute demyelinating polyradiculoneuropathy can be due to multiple causes. SP can be one of its etiologies and occur at infrequent ages and localizations.     

POEMS syndrome with plasmocytoma lytic bone lesion

INTRODUCTION: Crow-Fukase or Polyneuropathy, Organomegaly, Endocrinopathy, M-protein, and Skin changes syndrome (POEMS) is a rare multisystemic affection with incompletely elucidated etiopathogenesis. CASE REPORT: We report a case of POEMS syndrome in a 48-year-old adult revealed four months before admission by areflexic flask tetraparesis prevalent on the lower limbs in connection with demyelinating and axonal CIDP "like" sensoriomotor neuropathy of the four limbs electroneuromyographically. The patient presented elevated protein level in the CSF with monoclonal standard IgG gammapathy associated with a narrow band lambda, suggesting POEMS syndrome. Further explorations revealed skin lesions with glomeruloid angiomas, edematous vasomotor disorders as well as erythrocyanose, hypogonadism, papillar edema and a lytic bone lesion of the left scapula. Radiotherapy was associated with corticosteroids and plasma exchanges. Outcome was good with resolution of the symptoms and stabilization of the neuropathy. DISCUSSION: POEMS syndrome is rare; the diagnosis is based on necessary criteria, the presence of a demyelinating and axonal polyneuropathy associated with an IgA or IgG monoclonal gammapathy, the light chain being almost entirely lambda, associated to other characteristic elements, in particular glomeruloid angiomas, endocrinopathy, sclerosing plasmocytoma which must be carefully required. Treatment is based on surgical cure or radiotherapy for bone lesion and non specific treatments such as corticosteroid therapy, plasma exchanges and IVIG.     

Antiphospholipid syndrome and dystonia-parkinsonism. A case report

Background: Although clinically evident and MRI confirmed, basal ganglia involvement, is usual in primary antiphospholipid syndrome, extrapyramidal disorders such as parkinsonism and dystonia are very rare. We were unable to find any report in the literature on dystonia-parkinsonism in patients with primary antiphospholipid syndrome. Here we report an adult patient with dystonia-parkinsonism and primary antiphospholipid syndrome.Case report: A 60 year old, right-handed man came to our attention due to writer's cramp, bradykinesia and stiffness of his right hand. Neurological examination revealed constant, marked dystonic posturing, rigidity and bradykinesia of the right hand. Hyper-gammaglobulinemia was demonstrated on electrophoresis-serum IgG was increased. Anticardiolipin antibodies were examined by counterimmunoelectrophoresis (ELISA): IgG was negative, while IgM was positive. There was also slight thrombocytopenia. Magnetic resonance imaging brain scan axial T2W/UTSE revealed several hyperintense lesions in the basal ganglia and in the periventricular white matter and diffuse hyperintensity of the subcortical white matter bilaterally in the parietal regions. There was asymmetric parenchimal atrophy, more prominent in the left hemisphere. No clinical improvement was achieved by levodopa, dopamine agonists or anticholinergics. According to the criteria for primary antiphospholipid syndrome our patient had thrombocytopenia and high levels of IgG and IgM anticardiolipin antibodies so he was presumed to have a primary antiphospholipid syndrome.Conclusion: Various movement disorders may appear secondary to stroke, antiphospholipid syndrome, Behcet's disease or brain tumor. These cases may help in the understanding of pathophysiology of movement disorders. Dystonia and parkinsonism as well as other movement disorders may be associated with primary antiphospholipid syndrome.     

Increased vascular endothelial growth factor (VEGF) is causative in Crow-Fukase syndrome]

Crow-Fukase syndrome is a rare multisystem disorder characterized by polyneuropathy, organomegaly, endocrinopathy, skin changes and M-protein. We have examined levels of vascular endothelial growth factor/vascular permeability factor (VEGF) in serum with Crow-Fukase patients. Serum VEGF levels in Crow-Fukase syndrome were about 15 to 30 times higher than control and other neurological disorders. Most of the characteristic manifestations may be well explainable by the biological function of VEGF except polyneuropathy. We examined the direct effects of VEGF on blood nerve barrier function using blood brain barrier model of rat and intraneural injection of recombinant VEGF. As the result, VEGF affected blood nerve barrier and increased microvascular permeability, thereby inducing endoneurial edema. After increasing the permeability of the blood nerve barrier by VEGF, serum components toxic to nerves such as complements and thrombins may induce nerve damage. Our results suggest that overproduction of VEGF plays an important role in the pathogenesis of Crow-Fukase syndrome.     

Clonal restriction of platelet-associated anti-GPIIb/IIIa autoantibodies in patients with chronic ITP

Chronic immune thrombocytopenic purpura is due to platelet destruction induced by autoantibodies against platelet surface antigens. Prior studies show that some serum autoantibodies are light-chain restricted, suggesting a clonal origin. Since plasma and platelet-associated antibody from the same patient may bind to different epitopes. it is important to evaluate the clonality of platelet-associated antibody. Platelet-associated autoantibodies from 28 ITP patients were studied. Of 23 platelet-associated antibodies tested directly, 16 showed significant light chain restriction (7 complete and 9 partial) when compared to plasma IgG light chain distribution. Similarly, 9 of 12 platelet-associated antibody eluates were light chain restricted, 5 complete and 4 partial. In all cases where platelet-associated antibody and antibody eluate from the same patient were studied, the results were concordant. We conclude that a significant proportion of platelet-associated antibodies from ITP patients show apparent clonality, as evaluated by light chain restriction. These results are consistent with other studies in ITP suggesting a limited antigenic repertoire.     

Platelet-mediated proteolytic down regulation of the anticoagulant activity of protein S in individuals with haematological malignancies

The natural anticoagulant protein S contains a so-called thrombin- sensitive region (TSR), which is susceptible to proteolytic cleavage. We have previously shown that a platelet-associated protease is able to cleave protein S under physiological plasma conditions in vitro . The aim of the present study was to investigate the relation between platelet-associated protein S cleaving activity and in vivo protein S cleavage, and to evaluate the impact of in vivo protein S cleavage on its anticoagulant activity. Protein S cleavage in healthy subjects and in thrombocytopenic and thrombocythaemic patients was evaluated by immunological techniques. Concentration of cleaved and intact protein S was correlated to levels of activated protein C (APC)-dependent and APC-independent protein S anticoagulant activity. In plasma from healthy volunteers 25% of protein S is cleaved in the TSR. While in plasma there was a clear positive correlation between levels of intact protein S and both APC-dependent and APC-independent protein S anticoagulant activities, these correlations were absent for cleaved protein S. Protein S cleavage was significantly increased in patients with essential thrombocythaemia (ET) and significantly reduced in patients with chemotherapy-induced thrombocytopenia. In ET patients on cytoreductive therapy, both platelet count and protein S cleavage returned to normal values. Accordingly, platelet transfusion restored cleavage of protein S to normal values in patients with chemotherapy-induced thrombocytopenia. In conclusion, proteases from platelets seem to contribute to the presence of cleaved protein S in the circulation and may enhance the coagulation response in vivo by down regulating the anticoagulant activity of protein S.