Yueh-Feng  Sung

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.

DISCUSSION:
Herein, we described a rare case of a 33-year-old woman with anti-SRP myopathy associated with axonal sensorimotor polyneuropathy. Muscle strength increased in the lower limbs, and muscle enzymes decreased significantly after treatment with corticosteroids and azathioprine, but axonal degeneration of the lower limbs persisted. The patient presented with proximal weakness in the lower limbs with a waddling gait, which was clinically indicative of myopathy. However, lower-limb paresthesia and areflexia indicated a possible neuropathy, which was confirmed by NCS. Peripheral nervous system involvement is observed in some autoimmune diseases, such as systemic lupus erythematosus, systemic scleroderma, and Sjogren’s syndrome (15). Furthermore, combined myopathy and polyneuropathy have been reported in dermatomyositis and polymyositis (15-17). Vasculitis, paraneoplastic origin, and viral disease have been included in the pathogenic hypothesis of neuromyositis (5, 17). A literature review revealed that only a few cases of anti- SRP myopathy complicated by polyneuropathy have been reported (Table 2) (18-20). One patient was thought to have an overlap of Miller Fisher syndrome, axonal Guillain– Barre syndrome, and Bickerstaff’s brainstem encephalitis (18). Another patient had dysphagia, respiratory failure, and cardiac failure in addition to muscle weakness (20). The prognosis was poor in both cases. Our patient’s overall response to immunosuppressants was fair, as her muscle power increased, and clinical data, including muscle enzymes and liver function, improved substantially. While most patients with anti-SRP myopathy experienced rapid progression of symptoms (8, 13, 14, 18), our patient had good recovery with a fair response to immunosuppressive therapy. The phenomenon was also observed in some cases (21, 22). However, elevated CK levels demonstrated that most patients with anti- SRP myopathy indicated continued disease activity after immunosuppressive therapy, despite improvement in strength (8). In our patient, muscle biopsy failed to obtain adequate muscle tissue for pathological analysis and revealed only a predominance of fibroadipose tissue with mixed inflammatory cell infiltrations. A previous study reported that performing a muscle biopsy in edematous regions increases the likelihood of obtaining a diagnostic biopsy, whereas nondiagnostic biopsies may be more likely when a non-edematous or fat-replaced muscle is selected (4). The patient was diagnosed with anti-SRP myositis based on serological (anti-SRP antibody) and clinical criteria (high CK and proximal weakness). In the European Neuromuscular Centre criteria, muscle biopsy is not strictly required for diagnosing anti-HMGCR or anti- SRP myopathy. However, muscle biopsy is required for diagnosing an antibody-negative IMNM (4).