Diagnostic usefulness of intramuscular nerve bundles.

The diagnostic usefulness of pathological changes in intramuscular nerve bundles was assessed in 555 consecutive muscle biopsy specimens. Nearly half (45%) of the biopsy specimens contained at least six nerve fibers. Slight endoneurial fibrosis was present in all biopsy specimens from patients over age 10 years. Moderate or marked fibrosis was infrequent in patients lacking electrodiagnostic, clinical, or muscle biopsy evidence of denervation but was present in 90% or more of patients with either spinal muscular atrophy or peripheral neuropathy; fibrosis correlated well with the presence of muscle fiber type grouping and grouped atrophy. Specific pathological diagnoses suggested by nerve bundles included amyloid, dysglobulinemic, and hypertrophic neuropathies.