Purpose: Anti-signal recognition particle (SRP) myopathy is a subtype of immune-mediated necrotizing myopathy. It rarely presents with extramuscular features, involving the skin, lung, and heart. This paper presents a case of anti-SRP myopathy associated with sensorimotor polyneuropathy.
Case report: A 33-year-old woman with no history of systemic disease presented to our hospital with weakness and numbness of the lower limbs for 1 year. Electromyography and nerve conduction study (NCS) revealed combined myopathy and axonal sensorimotor polyneuropathy. Blood examination revealed increased levels of serum muscle enzymes and anti-SRP antibodies. T1-weighted magnetic resonance imaging revealed diffuse muscular hyperintensities in the thighs, indicative of fatty replacement. She was administered methylprednisolone pulse therapy, followed by oral prednisolone and azathioprine. Muscle power increased, and serum muscle enzyme levels decreased significantly. Subsequent NCS performed 2 years later revealed persistent axonal degeneration in the lower limbs.
Conclusion: Anti-SRP myopathy can present with sensorimotor polyneuropathy. Thus, the possibility that the same pathological process affected the skeletal muscles and peripheral nerves should be considered.
Keywords: anti-SRP myopathy; immune-mediated necrotizing myopathy; sensorimotor polyneuropathy..