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[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.