Morvan's fibrillary chorea, Morvan's syndrome, neuromyotonia NMT, and Isaac syndrome


Morvan’s ‘fibrillary chorea’ a.k.a. Morvan’s syndrome, neuromyotonia NMT a.k.a. Isaac syndrome:

  • Both conditions have been described with anti-voltage-gated potassium channel antibodies anti-VGKC (Kv1)
  • VGKC is positive in patients with limbic encephalitis, Morovan’s syndrome. These have different targets.
  • Caspr2: contactin-associated protein-antibody-2, a subtype of VGKC found in Morovan’s syndrome
  • Lgi1: leucine-rich, glioma inactivated 1 protein, a subtype of VGKC found in limbic encephalitis.

Morvan syndrome:


Clinical features: neuromyotonia (myokymia with cramping), hyperhidrosis and disordered sleep. Other features pain, weight loss, severe insomnia and hallucinations.
Fibrillations and myokymia may also occur.

Neuromyotonia NMT a.k.a. Isaac syndrome a.k.a Isaac’s-Merten’s syndrome a.ka. acquired neuromyotonia a.k.a. continuous muscle fiber activity syndrome a.k.a. quantal squander syndrome:


This is determined by clinical features, plus EMG findings and antibody testing

Clinical features:

neuromyotonia (myokymia with cramping, that isn’t elicited by muscle percussion), without CNS manifestations
Fibrillations and myokymia may also occur.


Neuromyotonia i.e. abnormal spontaneous activity of a single motor unit potential at 150-250 Hz (very high) with a decrementing response. “pinging” sound on EMG. MUAP morphology.


Phenytoin PHT P.O.
Or Carbamazepine CBZ P.O.

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