2nd September 2020

A 40 year old woman presents to you with a 3 month history of trunk weakness

A 40 year old woman presents to you with a 3 month history of trunk weakness. Her main complaint is difficulty in climbing stairs and lifting heavy objects. The weakness has fluctuated over the 3 months, being better some weeks than others. On neurological examination there is no abnormality of fine motor movement or in the distal muscles. A diagnosis of polymyositis is considered. 

Which investigation would be diagnostic of polymyositis? 

Select the SINGLE most appropriate option from the list below. Select ONE option only.