(Morvan fibrillary chorea,  limbic encephalitis-neuromyotonia-hyperhidrosis-polyneuropathy syndrome)

Incidence: 1/106. Acquired neurological disease caused by the presence of autoantibodies directed against the voltage-dependent K-channels that results in hyperexcitability of the peripheral nerves. It could be a variant of Isaacs syndrome (see this term). It mainly affects young men. Morvan's disease can present in different ways depending on its severity.

There are four levels of involvement:

• first level: benign but painful fasciculations  (especially in the face and the tongue) (myokimias) called "neuromyotonia"
• second level: muscle hypertonia with painful cramps (lower limbs), dystonia
• third level: muscle stiffness, sometimes spontaneous laryngeal spasm
• fourth level: central nervous system involvement (delirium, hallucinations, confusion, severe insomnia) associated with dysautonomy (changes in blood pressure, hyperhidrosis). Sometimes: cardiac rhythm disorders.

Weight loss, pruritus and fever are frequently observed.

EMG: pseudomyotonia.

A thymoma is present in more than 50 % of cases, what makes that this syndrome is often considered as paraneoplastic

Treatment: antiepileptics (carbamazepine, valproate), plasmapheresis, thymectomy.

Anesthetic implications:

Avoid succinylcholine. Titration of non-depolarizing muscle relaxants: one may encounter sensitivity or resistance to their effects. The results of the spectral analysis of the EEG (BIS) may be alterated by the presence of myokimias (artificial elevation). Use direct-acting vasopressors to manage the tensional lability associated with the dysautonomy. Risk of spontaneous laryngospasm.  Increased risk of post-operative respiratory complications (aspirations facilitated by the myotonic crises of the laryngeal muscles).

References :

-        Tufail S, Stacey M.
General anaesthesia in a patient with Morvan’s syndrome.
Anaesth Cases 2013; 1: 97-8.

-        Royston SE, Hartigan PM.
Anesthetic management of robotic thymectomy in a patient with Morvan syndrome: a case report.
A&A Practice 2021; 15: e01383

Updated: January 2021