Immunohistochemical detection of complement factors: a reliable method forthe diagnosis of myasthenia gravis

A 57-year-old woman suffered from generalized muscular weakness without dip lopia or dysphagia for about 2 years. An abnormal decremental response on l ow frequency nerve stimulation and improvement upon administration of edrop honium chloride suggested a diagnosis of myasthenia gravis. However,this di agnosis remained uncertain, since repeated tests for antiacetylcholine rece ptor antibodies were negative. In addition, the patient reported that she w as never able to keep up with peers in prolonged physical activities since childhood. For this reason, a congenital myasthenic syndrome was suspected and an intercostal muscle biopsy performed for special end-plate studies. I mmunohistochemistry of the muscle biopsy revealed membrane attack complex d eposits at the end-plates. This finding definitely confirmed the diagnosis of autoimmune myasthenia gravis. In conclusion, immunohistochemistry for co mplement deposits at the end-plates is a simple and reliable method of conf irming the diagnosis of myasthenia gravis in uncertain cases.