Inclusion body myositis in Connecticut - Observations in 35 patients during an 8-year period

Sporadic inclusion body myositis (IBM) is the most common acquired myopathy in patients older than 50 years. In order to provide information on the prevalence rate, presenting signs and symptoms, and disease progression of IBM in Connecticut, we reviewed the medical records, electromyography reports, and muscle histopathology of 35 patients with the diagnosis of definite or possible IBM evaluated at our neuromuscular referral center during an 8-year period (1992-2000). There were 23 men and 12 women; the mean age at examination was 70.0 years (range, 50-85 yr) and at onset, 64.3 years (range, 41-80 yr). The mean latency between symptom onset and IBM diagnosis was 5.7 years (range, 1-25 yr). The prevalence rate of IBM was 10.7 × 10-6 for all patients, 14.5 × 10-6 for men, and 7.1 × 10-6 for women. The age-adjusted prevalence rate for age 45 years and older was 28.9 × 10-6. Eighty-six percent of patients were referred with other diagnoses; the most common misdiagnosis was motor neuron disease. At presentation, the greatest weakness was observed in the knee extensors, finger flexors, and ankle extensors. Symptoms of dysphagia were noted in 54%. For 8 patients followed during 4 years, the decline in the mean upper extremity strength was 3.5% per year (0.3% per month), in mean lower extremity strength, 3.6% per year (0.3% per month), and in mean grip strength, 10.7% per year (0.9% per month).