Isaacs syndrome
Clinic
- A clinical syndrome in which generalized myokymia was a prominent component
- Spontaneous motor activity was the distal segments of peripheral nerves, since it was not eliminated by blockade of the peripheral nerve but could be eliminated by curare
- Facial myokymia was first described clinically in 1902 by Bernhardt. Then, in 1948, Denny-Brown and Foley first described generalized myokymia and identified the electrical correlate of this activity, consisting of continuous irregular discharges from motor units. Later, the term neuromyotonia was coined by Mertens and Zschocke to highlight the myotonialike muscle spasms and the peripheral nerve origin.
More recently, VGKC complex autoantibodies were identified in many patients with Isaacs syndrome. In some, the disorder is considered paraneoplastic since it is associated with a neoplasm, mainly thymoma and small cell lung cancer, usually associated with VGKC complex autoantibodies. The disorder is sometimes referred to as acquired neuromyotonia or idiopathic generalized myokymia. Isaacs syndrome is the preferred term, since both myokymia and neuromyotonia may be seen in other disorders (Table 11-1 and Table 11-2). Isaacs syndrome may affect patients at any age and varies significantly in severity. In most cases, it manifests with generalized muscle stiffness (neuromyotonia) and slowness of movement (Case 11-1). The stiffness persists during sleep. Clinical manifestations include muscle hypertrophy (mainly calf muscles), continuous muscle twitching, and undulation (myokymia). Trousseau and Chvostek signs may also be present. Dysarthria and dysphagia may occur when abnormal muscle activity affects bulbar muscles. In severe cases, muscles and posture may be rigid. Signs of dysautonomia, including hyperhidrosis, sialorrhea, piloerection (goose flesh), and abdominal pain, are frequent. Sensory manifestations are rare but may include paresthesia and neuropathic pain. The clinical symptoms of Isaacs syndrome may fluctuate but are usually slowly progressive over years.