Limb-girdle myasthenia is a rare form of autoimmune myasthenia which presents without the typical ocular or bulbar symptoms. Patients present with proximal muscle weakness and are often misdiagnosed as a myopathy and tests for myasthenia may not always be performed.
This 43-year-old lady presented with “legs giving way” while climbing stairs or bending down. She was initially investigated by the rheumatologists who noted a marginally increased creatine kinase level (263). A muscle biopsy which showed tubular aggregates on gomori trichrome staining and cylindrical spirals on electron microscopy. She was referred for a neuromuscular opinion.
Neurophysiology showed decremental response (60.7%) on repetitive nerve stimulation and a prolonged jitter (mean MCD –60 mcs) on SFEMG. AChR antibodies were strongly positive at 344 nM (confirmed using multiple assays in different labs). She responded well to pyridostigmine therapy, but no additional response to steroids was noted. In view of the atypical presentation several possible genetic mutations were tested (mitochondrial, GFPT1, DPAGT1) which were all negative.
Autoimmune limb-girdle myasthenia is a very rare sub-type of myasthenia which may not respond as well to immunosuppressive therapy. Unusual muscle biopsy findings suggest that there might be non-immunological reasons playing a part in the pathophysiology of this disease.
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