[THE VALUE OF MUSCLE BIOPSY IN PATIENTS WITHOUT WEAKNESS, HIGH CREATINE KINASE OR MYOPATHY ON ELECTROMYOGRAPHY].

INTRODUCTION: Muscle biopsy is an important diagnostic procedure for the evaluation of neuromuscular disorders, commonly employed when patients present with muscle weakness, high creatine-kinase or electromyography which suggest myopathy. The diagnostic value of this procedure when these are normal is unclear. AIMS: To characterize the pathology in muscle biopsies of patients without clinical, laboratory or electromyographic suggestion for myopathy. METHODS: Retrospective chart and pathology review of consecutive patients who were evaluated by muscle biopsy at Sheba Medical Center. RESULTS: Of 109 patients, 12 (11%) had no indication for myopathy prior to biopsy. Pathology was identified in 2/3 of cases. Inflammation was detected in 5 cases (42%), with a perivascular infiltrate in four, and endomysial in one. A mild myopathy was present in 3/5 of these cases. Type-2 muscle fiber atrophy as the primary or only pathology was seen in 2 cases (17%) and mild neurogenic changes in one (8%). A history of systemic disease, additional laboratory tests or imaging suggestive for inflammation were predictive for inflammatory pathology in 4/5 of cases (P = 0.006). CONCLUSIONS: Perivascular inflammation without significant muscle fiber damage is common and meaningful in patients with inflammatory conditions in spite of normal evaluation for myopathy. DISCUSSION: Muscle disease is characterized by damage to muscle fibers, connective tissue or vessels. In the absence of fiber damage, muscle strength, creatine-kinase and electromyography may remain normal. These tests therefore do not rule-out perivascular inflammation and mild myopathy. Muscle biopsy is effective for the detection of inflammation in patients with inflammatory conditions in spite of normal strength creatine-kinase and electromyography.