Atypical Miyoshi distal myopathy: A case report

Abstract

Five distinct predominant distal myopathies have been identified with discrete clinical and genetic patterns. Miyoshi myopathy (MM; early adult-onset, type 2) is a subtype of dysferlinopathy. Furthermore, MM is the most common form of autosomal recessive distal myopathy. MM is typically characterized by muscular weakness, initially affecting the gastrocnemius or soleus muscle from the late teens or early adulthood. The present study reports a case of MM that was confirmed by pathological and immunohistochemical methods, in addition to a review of the relevant literature. A 37-year-old male patient presented with muscular weakness in the left foot. This clinical manifestation was not typical of MM, and the patient was initially diagnosed with inflammatory myopathy. He was treated with dexamethasone at a dose of 10 mg for 5 days followed by gradual tapering, following which the symptoms were alleviated; however, the pathology, immunohistochemistry and electromyography eventually confirmed the diagnosis of MM. The treatment was then terminated and the patient was discharged. The present study further supports the underlying heterogeneity in atypical MM-like phenotypes. Dysferlin protein deficiency can be identified by pathological examination. The pathology of dysferlinopathy is characterized by changes of muscular dystrophy. Inflammatory cellular infiltration is a relatively common finding in the muscle biopsies from numerous patients with dysferlinopathy. Therefore, the detection of dysferlin deficiency or marked reduction on the sarcolemma using immunohistochemical staining is important for the diagnosis of dysferlinopathy.

Keywords: atypical distal Miyoshi myopathy; case report; immunohistochemistry staining.

Figure 1.

Photomicrographs showing the results of various stains. (A) Muscle fiber size ranged markedly (hematoxylin and eosin staining; magnification, ×200). (B) No ragged red muscle fibers, rimmed vacuoles and intramuscular nerve (modified Gomori trichrome staining; magnification, ×200). (C) No fiber enzyme activity (cytochrome oxidase staining; magnification, ×200). (D) No ribosome biogenesis factors and spindle-shaped viruses (succinate dehydrogenase staining; magnification, ×200). (E) Mesh structure between myofibrils was normal (nicotinamide adenine dinucleotide-tetrazolium reductase staining; magnification, ×200). (F) Muscle fibers were not increased (periodic acid-Schiff staining; magnification, ×200). (G) No increased muscle fibers within the content of lipid droplets (Oil Red O staining; magnification, ×200). (H) Two types of fibers distributed alternatively (adenosine triphosphatase staining; magnification, ×200).

Figure 2.

Immunohistochemical staining shows positive (A) dystrophin-C, (B) dystrophin-N and (C) dystrophin-R staining and (D) total absence of dysferlin labeling. Magnification, ×200.