Qualitative and quantitative modifications of von Willebrand factor in patients with essential thrombocythemia and controlled platelet count

BACKGROUND

Essential thrombocythemia (ET) is characterized by increased platelets and prevalent thrombosis. An acquired von Willebrand factor (VWF) disease has been hypothesized and inconsistently associated with extreme thrombocytosis or rare bleeding in ET. Whether VWF is modified in ET patients with controlled platelet count remains unclear.

OBJECTIVES

We studied different VWF- and platelet-associated parameters in ET patients treated according to current recommendations.

PATIENTS/METHODS

Sixty-nine ET patients (M = 29; median age, 62 [48-70] years; platelets, 432 [337-620] × 10(3)  μL(-1) ), 69 matched controls and 10 subjects with reactive thrombocytosis (RT) were studied. VWF:antigen (Ag), activity (act), electrophoretic patterns, VWF:propeptide, plasma glycocalycin (GC), glycoproteinV (GpV), ADAMTS-13, elastase, C-reactive protein and serum thromboxane (TX)B2 were measured.

RESULTS

In ET patients, VWF:Ag was increased by 31 ± 13% vs. controls (P < 0.01), without dependence of blood groups, while VWF:act was reduced by 21 ± 12% vs. controls and by 50 ± 24% vs. RT (P < 0.01). The VWF:act/VWF:Ag ratios in ET were reduced by 35 ± 17% vs. controls and RT patients (P < 0.001) and significantly associated with: immature or total platelet counts, GC, GpV and TXB2 . In multivariable analysis, only GC inversely predicted ET patients' VWF:act/VWF:Ag ratios (β = -0.42, P = 0.01). By electrophoresis analyses, high-molecular-weight VWF multimers were variably reduced with atypical cleavage bands in ET only. VWF:propeptide, ADAMTS-13 and elastase levels were normal in ET patients. Platelet-associated ADAM-10 and ADAM-17 hydrolyzed VWFm in vitro, showing patterns similar to those in ET samples.

CONCLUSIONS

In ET patients with controlled platelet counts, the VWF:act/VWF:Ag ratio is decreased and predicted by GC, a product of platelet activation. ADAM-10 and/or ADAM-17 might be involved. In vivo platelet activation, which characterizes ET, might contribute to disease-specific VWF alterations.

Experience from a multidisciplinary "dizzy" clinic

OBJECTIVE

To describe the experience of a combined otolaryngology and neurology multidisciplinary clinic in the evaluation, investigation, and management of patients with dizziness.

STUDY DESIGN

Prospective clinical study.

SETTING

Patients were seen in a tertiary referral, multidisciplinary clinic at The Toronto Hospital, University of Toronto, Ontario, Canada.

INTERVENTION

A thorough history, formal otoneurologic examination, and appropriate laboratory investigations were performed. After their assessment, the patient's diagnoses were classified as peripheral, central, psychogenic, or undiagnosed and were then subdivided into specific clinical diagnoses.

RESULTS

The first 812 consecutive patients seen in the multidisciplinary clinic from January 1, 1993 to December 31, 1998 are reported. Five hundred twenty-five (64.7%) patients were found to have a peripheral vestibular cause for their dizziness, 66 (8.1%) had a central cause, 108 (13.3%) had a diagnosis unknown, and 73 (9.0%) were thought to be psychogenic. In 40 (4.9%) patients, a peripheral and central cause were found. More than one type of peripheral disorder was noted in 17.9% of patients with a peripheral vestibular cause for their dizziness, and 12.3% of patients with a central cause for their dizziness had more than one specific type of central nervous system disorder.

CONCLUSIONS

Most patients that were seen in a multidisciplinary clinic had a peripheral vestibular disorder. Central causes of dizziness were relatively uncommon. Serious diseases such as tumor, multiple sclerosis, and encephalitis were rare and unlikely to present with dizziness only. It is important to realize that a patient may have more than one type of disorder accounting for the symptoms, which may represent a spectrum of disease affecting the inner ear.

Evaluation of the dizzy patient: experience from a multidisciplinary neurotology clinic

In 1993 a multidisciplinary neurotology clinic was established at the Toronto Hospital, University of Toronto, where patients with symptoms of dizziness were assessed by both otolaryngologists and neurologists. The results from the first 400 patients seen in consultation are described. The disease pathologies identified in this patient population with dizziness showed some significant differences from other published series, which we believe reflects the specialized tertiary nature of referrals to this clinic. A model for the collaborative investigation of the dizzy patient is provided consistent with the current trend towards multidisciplinary approaches in medicine.