A prior EMG was reported as normal. Genetic testing for myotonic dystrophy was normal. If necessary, revise your differential diagnosis based on the additional physical findings. Design your approach to the electrophysiologic examination based on the existing data. Serologies are essentially normal and rule out hypocalcemia and hypomagnesemia, as well as a myopathic process.
Myotonic dystrophy is ruled out based on genetic testing.
Congenital myotonia remains in the differential diagnosis and myotonic discharges should be sought on electrodiagnostic testing, including needle examination on a cooled limb muscle. Stiff person syndrome is characterized by normal nerve conduction studies. Needle examination is typically normal and the evaluation of a muscle during a spasm reveals continuous motor unit activity associated with normal motor unit action potentials.