Electrophysiological characteristics in four patients from Brazil with stiff person syndrome.

Stiff person syndrome (SPS) is a rare immune-mediated disorder of the central nervous system characterized by muscle rigidity and episodic muscle spasms. The diagnosis of SPS is based on electrophysiological studies. We analyzed the electrophysiological features in four patients from Brazil who fulfilled the clinical criteria for SPS. The most common electrophysiological abnormalities were continuous motor unit activity, co-contracting, and the presence of the cutaneomuscular reflex. Despite all patients having clinical characteristics of SPS during the disease, no patient met all the electrophysiological criteria for SPS even after repeat electrophysiological studies. This shows that a diagnosis of SPS should not be restricted to patients with all the classic electrophysiological changes but should be considered in the presence of one or some of those changes.