Quiz Form

Question Date: 04/09/2023

Question: Which of these statements is not true regarding neuromyotonia (Isaacs syndrome)?

Options:

• Generalized muscle stiffness (neuromyotonia) abates in sleep
• It is caused by autoantibodies to CASPR2
• It may be associated with thymoma
• Autonomic changes like hyperhidrosis and neuropathic pain are common

Correct Answer: Generalized muscle stiffness (neuromyotonia) abates in sleep

Explaination: Isaacs syndrome or neuromyotonia presents with muscle stiffness that persists in sleep and anesthesia unlike stiff person syndrome. Muscle rippling (myokymia), autonomic dysfunction (hyperhidrosis, sialorrhea) and neuropathic pain are seen. Sleep disturbance suggests morvan syndrome. Electrophysiology may show myokymia (doublets and triplets) or neuromyotonic discharges. It is associated with autoantibodies to voltage gated potassium channels (VGKC) These are directed against LGI1 (limbic encephalitis) and CASPR2 (neuromyotonia), although overlap may occur. CASPR2 is associated with thymoma in up to 20% of cases

Reference: Sawlani K et al. Peripheral Nerve Hyperexcitability Syndromes. Continuum 201723(5)1437-1450.