Which histologic findings are characteristic of focal muscular atrophy (FMA)?

Updated: Feb 20, 2018
  • Author: Sridharan Ramaratnam, MD, MBBS; Chief Editor: Helmi L Lutsep, MD  more...
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Answer

Histologic findings are dependent on the underlying cause. Necropsy in one patient with monomelic amyotrophy [26] (who died of unrelated causes) revealed lesions only in the anterior horns of the spinal cord over a few segments. The anterior horn cells showed shrinkage and necrosis, various degrees of degeneration of large and small neurons, and mild gliosis. The posterior horn, white matter, and vascular system showed no abnormalities.

Autopsies of a few patients with PPMA [54] revealed the presence of persistent or new inflammation (lymphocytic infiltrates) in the meninges, spinal cord, and muscles of affected patients. In one of these patients, immunoperoxidase staining demonstrated that the inflammatory infiltrates were virtually pure populations of B lymphocytes. The other histologic features were the presence in spinal cord anterior horns of axonal spheroids and Wallerian degeneration in the lateral columns. No abnormalities were found in the brain. In patients with chronic disease, muscle histology in focal myositis may reveal variable fiber size, degenerating and regenerating fibers, inflammatory foci, vasculitis, and fibroblastic proliferation.

In Kennedy disease, the muscle biopsy specimen reveals variability of fiber size with groups of angular atrophic fibers, fiber type grouping, and pyknotic nuclear clumps characteristic of chronic denervation with reinnervation. Nonspecific myopathic features, including increased central nuclei and necrotic fibers, are also seen. The histopathologic hallmark is the presence of nuclear inclusions containing mutant truncated ARs in the residual motor neurons in the brainstem and spinal cord as well as in some other visceral organs.

The histologic findings in inclusion body myositis are endomysial inflammation, small groups of atrophic fibers, eosinophilic cytoplasmic inclusions, and muscle fibers with one or more rimmed vacuoles that are lined with granular material. Amyloid deposition is evident on Congo red staining by using polarized light or fluorescence techniques. Electron microscopy demonstrates 15-21 nm cytoplasmic and intranuclear tubulofilaments.

Muscle histology in sarcoidosis is characterized by perivascular noncaseating granulomas consisting of clusters of epithelioid cells, lymphocytes, and giant cells.

Muscle histology in injection myopathy may reveal perimysial and endomysial fibrosis with nonspecific degeneration, regenerative changes and, in some cases, partial denervation signs. Electron microscopy reveals that endomysial and perimysial collagen fibrils have lost their normal unimodal diameter distribution. They instead show a broad spectral distribution of diameters, suggesting defective control of collagen formation.


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