Is a Muscle Biopsy Necessary for the Diagnosis of Inclusion Body Myositis (IBM)? (P07.223)

Abstract

Objective: To determine if a muscle biopsy is superior or adds to the clinical diagnosis of inclusion body myositis. Background Inclusion body myositis is a mixed degenerative and inflammatory disease. There is no effective treatment. The diagnosis is confirmed by muscle biopsy showing congophilic deposits and rimmed vacuoles or by electronmicroscope showing the filamentous inclusions. Design/Methods: Twenty-one patients with clinical diagnosis of inclusion body myositis underwent muscle biopsy for confirmation. All patients had proximal and distal muscle weakness with preferential involvement of finger flexors and quadriceps muscles. Muscle biopsies were performed from a moderate weak muscle and were examined for the presence of rimmed vacuoles or congophilic deposits or both. Results: There were fourteen females and seven males. Average age at presentation was 60 years (35-80). CK level was elevated in 18 patients. Mean CK elevation was 942 U/L and ranged from 72-4774. Mean disease duration before the biopsy was 6 years and ranged from 1-15 years. The muscle biopsy confirmed the diagnosis in 15 patients. Six patients (5 females and 1 male) had no rimmed vacuoles or congophilic deposits detected on their muscle biopsies, but all patients had autoaggressive endomysial inflammatory response with mononuclear cells invading none necrotic muscle fibers. Ten patients had received different types of immunotherapy, but continued to deteriorate. Conclusions: 1- None of the patients suspecting to have IBM was found to have a different diagnosis.2- The muscle biopsy did not show the characteristic features of IBM in six patients.3- These findings question whether or not the muscle biopsy is necessary or add to the clinical diagnosis of inclusion body myositis.4-The clinical diagnosis of IBM remains superior to the muscle biopsy. Disclosure: Dr. Lee has nothing to disclose. Dr. Chahin has nothing to disclose.