Muscle biopsy findings in primary fibromyalgia and other forms of nonarticular rheumatism.

Virtually all the reports on muscle biopsy in chronic muscle pain conditions, except those of primary fibromyalgia syndrome (PFS) published recently, have inadequate methodologic information, particularly on definition of cases, and lack controlled materials, so that no firm conclusions may be made. A limited number of controlled studies of muscle biopsy in PFS suggest that results are negative by usual light microscopic, histochemical, and electron microscope examinations. The findings of abnormal rubber band-like structures and interconnecting network of reticular or elastic fibers in muscle fibers of certain PFS patients in a single study need to be confirmed by other centers by careful controlled and blinded observations. The findings that high-energy phosphate levels in tender PFS muscles are significantly reduced appear valid and important, and need to be independently confirmed by well-designed controlled and blinded studies. Finally, biopsy reports of unspecified or unclarified muscle pain syndromes should not be assumed to be those related to PFS, and such invalid references must be avoided.