Teaching video neuroimages: lid lag sign and diplopia in paramyotonia congenita.

Clinical bedside tests to provoke myotonia, such as eyelid closure, handgrip, and percussion myotonia, help to diagnose and differentiate myotonic disorders and prevent delayed genetic confirmation. Sodium channelopathies present with predominantly myotonia of the ocular muscles. In these cases, testing for myotonia of the upper eyelid and extraocular muscles could be of decisive diagnostic value. We present additional clinical bedside tests: the lid lag sign and provocation of short-term diplopia (video on the Neurology® Web site at Neurology.org and the figure). In our experience, these symptoms are especially present in paramyotonia congenita. Therefore, we advise to test for lid lag sign and short-term diplopia every time a myotonic disorder is suspected. AUTHOR CONTRIBUTIONS Dr. Stunnenberg: manuscript writing, clinical history taking, neurologic examination, and collection of videoimages, all under the supervision of Dr. Drost.