In addition, serum cholinesterase levels are needed to evaluate the potential for OP intoxication. The most important aspect of the examination are EMG studies, including needle EMG, nerve conduction velocities and repetitive nerve stimulation. In cases of suspected myasthenia gravis, response to edrophonium HCl, a short acting anticholinergic drug, can be used. On the other hand, it can worsen the signs of OP intoxication. For this reason, I prefer to perform edrophonium testing under anesthesia during the EMG procedure.
Idiopathic polymyositis is a diffuse inflammation of the skeletal muscles.
An autoimmune process is suspected, in most cases. There is generalized weakness which worsens on exercise. These patients also have a stiff stilted gait, lameness and pain on muscle palpation. Occasionally, generalized loss of skeletal muscle mass is evident. Megaesophagus may be present with regurgitation and aspiration pneumonia.