Diagnostic value of the muscle biopsy in the neonatal period.

Muscle biopsy specimens of 20 full-term neonates (13 surgical and seven necropsy specimens) with clinical evidence of neuromuscular disease were studied to determine the diagnostic usefulness of this procedure in the newborn. Characteristic pathologic alterations were identified in specific diseases. Some findings were similar to those seen later in life, but others differed from those expected in the same diseases at older ages. Persistence of fetal muscle cells was a characteristic common to several congenital myopathies and neuropathies. Lymphocytic infiltrates, muscle fiber necrosis, and architectural alterations of the muscle fibers were not seen at birth. Extramedullary hematopoiesis may involve newborn muscle. Muscle biopsy is a safe and simple procedure in the neonatal period and has a diagnostic reliability as good as at older ages, but histochemistry and sometimes electron microscopy are essential supplements to classical histology for interpretation. Recommended indications for muscle biopsy in the neonatal period are multiple joint contractures at birth or hypotonia and weakness, of unknown origin.