Muscle histopathology in today's era of molecular genetics: Role and limitations

Past few decades have seen an increasing application of techniques like electron microscopy, western blotting, and molecular genetics in the evaluation of muscle diseases. However, due to their limited availability, histopathological interpretation of muscle biopsies still remains an important component of diagnostic approach to muscle diseases. A systematic methodology is required in the evaluation and interpretation of muscle biopsies. This study was undertaken to analyze the histopathological spectrum of 164 muscle biopsies and to assess the diagnostic yield of basic histopathological procedures in the work up of muscle biopsy.

Retrospective analysis was done for 164 cases of muscle biopsies. Step-wise approach was adopted to assess the efficacy of routine stains, enzyme histochemistry, and immunohistochemistry. Based on hematoxylin and rosin (H and E) appearance, biopsies were broadly categorized into destructive, nondestructive but myopathic, and inflammatory morphology. Role of special stains, enzyme, and immunohistochemical stains in each category was then evaluated.

On the basis of histopathological features, 164 muscle biopsies were broadly categorized into biopsies with abnormal histopathological features (115) and biopsies with normal histopathology (49). Abnormal muscle biopsies were further categorized into destructive morphology (56.5%), nondestructive but myopathic morphology (30.5%), and inflammatory pathology (13%). A near definitive diagnosis could be made in 115 cases out of 164 muscle biopsies on the basis of routine histopathology, enzyme histochemistry, and immunohistochemistry.

Though advanced techniques like electron microscopy, western blotting, and molecular genetics are essential for confirmatory diagnosis, a substantive diagnostic yield can be offered with the basic armamentarium of routine (frozen) stains, enzyme histochemistry, and immunohistochemistry.