A 57-year-old woman with an 8-month history of generalized stiffness with episodic muscle spasms. The spasms began in both lower legs and spread onto the arms over a few months. Each of these lasted for about 30 minutes, with increasing frequency of up to 10 episodes per day. Between episodes, she is feeling stiffer and, as a result, slower. She has come to rely on a cane for ambulation given her fear of falls.

This middle-aged woman insidiously developed muscle rigidity and superimposed episodic spasms over several months. Examination showed markedly slowed movements due to the presence of rigidity with hyperreflexia without other upper motor neuron signs. She exhibited a cautious gait and exaggeration of normal lumbar lordosis. These features led to the suspicion of stiff person syndrome (SPS), which was confirmed by the identification of high titers of anti-glutamic acid decarboxylase (anti-GAD) antibodies. Clonazepam, increased to a dose of 1 mg four times a day, decreased the excessive rigidity, greatly reduced the frequency of the spasms, and improved her gait velocity and postural reflexes, as shown in the second video.

SPS is characterized by progressive muscular stiffness and gait difficulty with stimulus-sensitive superimposed painful muscle spasms leading to exaggerated lumbar lordosis and impaired ambulation, which progresses to becoming deliberate and slow, in part due to fear of falling (Fig. 17.1A-C). As shown in the video, the spasms may be spontaneous or stimulus sensitive and typically begin with an abrupt jerk, followed by tonic activity that slowly subsides over seconds to, less commonly, minutes. This is in contrast with the much faster exaggerated startle reaction of hyperekplexia, where brainstem hypersensitivity results from deficiency of glycine-mediated fast inhibitory postsynaptic potentials (IPSP) unlike the slow gamma aminobutyric acid (GABA)-mediated IPSP of SPS.