Document resource
A 73-year-old man presented with progressive weakness, leg cramps, dysphagia and weight loss. There was no obvert fluctuation to his symptoms. The patient was on low-dose atorvastatin for 6 years for hypercholesterolaemia. Examination revealed proximal muscle weakness, fatigable dysphonia and absent reflexes. His vital capacity was reduced.Nerve conduction studies was normal but with significant decrement on repetitive nerve stimulation. Electromyography demonstrated widespread active denervation, myotonia and myopathic units.Creatine kinase was 3,711(<250IU/L). HMGCR antibody was 31.0(<11.0 relative units) and ACHR antibody was >8(0-0.25nmol/L). Myositis immunoblot panel, autoimmune and infectious serology were negative. Whole-body positron emission tomography demonstrated no malignancy.Vastus muscle biopsy showed moderately extensive necrosis of single muscle fibres and no immune upregulation consistent with immune-mediated necrotizing myopathy (IMNM).The patient was treated with intravenous immunoglobulin and tapering prednisolone, resulting in gradual improvement in strength, bulbar and respiratory function and normalization of neurophysiology.The interaction between ACHR-antibody MG and HMGCR-antibody IMNM is very rare. Pathophysiology may be from the immunomodulatory effect of statins generating de-novo MG or unmasking MG. Alternatively, skeletal muscle necrosis in IMNM could result in self-epitope presentation, including ACHR. Clinicians should be aware of this rare overlap syndrome which may require tailored treatment considerations.victorzhang93@gmail.com