Teaching Video NeuroImages: Cold-induced laryngeal pseudomyotonia in Isaacs syndrome¶

Summary¶

• 36yo M
• c/c
  • progressive limb pain
  • excessive sweating
  • muscle cramps
  • transient strained voice only after cold water
• NeuroEx
  • gen myokymia
  • pseudomyotonia
• Ex
  • EMG
    • multi spontaneous, continuous high freq doublet / triplet motor unit discharge
  • NCS nl
  • CT (chest) nl
  • immune
    • CASPR2(–)
    • LGI1(–)
  • autoimmune / paraneo nl
• Tx
  • IV immunoglobline
  • CBZ
• Dx
  • Isaacs syndrome

Isaacs syndrome

• PN hyperexcitability disorder
• Ab targeting voltage-gated K ch (< 50% Ab(+))

Further¶

Terminology¶

• strain: 引っ張る, 精一杯努力する、 筋を違える
• myokymia: 筋波動症
• pseudomyotonia:
• Isaacs syndrome:

Original¶

A 36-year-old man developed progressive limb pain, excessive sweating, and muscle cramps. He described transient strained voice only after drinking cold water (video 1). Examination revealed generalized myokymia and pseudomyotonia. EMG revealed multiple spontaneous, continuous high frequency doublet and triplet motor unit discharges. Nerve conduction studies and chest CT scan were normal. CASPR2 and LGI1 antibodies were negative. Autoimmune, paraneoplastic, and other etiologies were excluded clinically as well as through additional serologic (or blood) testing and imaging. Symptoms resolved completely after IV immunoglobulin and carbamazepine for treatment of pain.

Video 1¶

A 36-year-old man with muscle cramps and transient strained voice

¶

Painful cramps, myokymia, hyperhidrosis, and pseudomyotonia are cardinal features of Isaacs syndrome. Isaacs syndrome is a peripheral nerve hyperexcitability disorder often associated with antibodies targeting components of voltage-gated potassium channels; however, <50% of patients are antibody-positive.¹ Bulbar involvement is an uncommon feature, and our patient exhibits cold-induced pseudomyotonia, which has not been previously described in the literature.²

References¶

1. Vincent A, Pettingill P, Pettingill R, et al. Association of leucine-rich glioma inactivated protein 1, contactin-associated protein 2, and contactin 2 antibodies with clinical features and patient-reported pain in acquired neuromyotonia. JAMA Neurol 2018;75:1519–1527.
2. Hart IK, Maddison P, Newsome-Davis J, Vincent A, Mills KR. Phenotypic variants of autoimmune peripheral nerve hyperexcitability. Brain 2002;125:1887–1895.

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