[A new type of periodic paralysis: Andersen-Tawil syndrome]. / Une nouvelle forme de paralysie périodique: le syndrome d'Andersen-Tawil.

Andersen-Tawil syndrome includes a clinical triad consisting of periodic paralysis, cardiac arrhythmia, and usually mild but diagnostically useful dysmorphic features. This potassium channelopathy is due to mutation of the KCNJ2 gene encoding the protein Kir 2.1. The main muscular manifestation is periodic paralysis, usually of the hypokalemic type. Muscle biopsy may reveal tubular aggregates or be normal, as in our patient. Cardiac manifestations are variable and may include a long QT syndrome, premature ventricular contractions, complex ventricular ectopy, and polymorphic or bidirectional ventricular tachycardia. Imipramine therapy had a positive effect on arrhythmia in our patient. Dysmorphic features provide a diagnostic clue but may be difficult to identify and should thus be methodically sought. Clinical expression is variable, even within the same family. Since the culprit gene KCNJ2 was identified, locus heterogeneity has been shown in Andersen-Tawil syndrome. Kindreds without KCNJ2 mutations are clinically indistinguishable from those with mutations. Kir2.1 is an inward rectifier K+ channel with important roles in maintaining membrane potential and during the terminal phase of cardiac action potential repolarization. Several studies show a dominant negative effect of KCNJ2 mutation on Kir 2.1 channel function.

Force assessment in periodic paralysis after electrical muscle stimulation.

OBJECTIVE: To obtain an objective measure of muscle force in periodic paralysis, we studied ankle dorsiflexion torque during induced paralytic attacks in hyperkalemic and hypokalemic patients. SUBJECTS, PATIENTS, AND METHODS: Dorsiflexor torque after peroneal nerve stimulation was recorded during provocative tests on 5 patients with hypokalemic or hyperkalemic disorders and on 2 control subjects (1995-2001). Manual strength assessment was simultaneously performed in a blinded fashion. Standardized provocation procedures were used. RESULTS: The loss of torque in hyperkalemic patients roughly paralleled the loss of clinically detectable strength, whereas in the hypokalemic patients, pronounced torque loss occurred well before observed clinical effects. No dramatic changes occurred in the control subjects. Torque amplitude decreased more than 70% in all patients during the provocation tests; such decreases were associated with alterations induced in serum potassium concentrations. CONCLUSIONS: Stimulated torque measurement offers several advantages in characterizing muscle dysfunction in periodic paralysis: (1) it is independent of patient effort; (2) it can show a definitely abnormal response early during provocative maneuvers; and (3) characteristics of muscle contraction can be measured that are unobservable during voluntary contraction. Stimulated torque measurements can characterize phenotypic muscle function in neuromuscular diseases.

[Andersen syndrome. Description of a case] . / Síndrome de Andersen. Descripción de un caso.

A 17 year-old man, with periodic muscular weakness since the age of 6 years, is presented. The episodes of periodic paralysis were of variable duration, from 1 to 3 days, and were induced by physical exercise or by stress. Weakness was generalised, although predominant in anterior compartment of the legs, with foot drop. Interictal neurological examination was absolutely normal. He showed dysmorphic features, with micrognatia. Cardiac examination revealed continuous arrhythmia. Basal EKG and 24 hours EKG-Holter confirmed the existence of abundant ventricular extrasystoles, with episodes of ventricular tachycardia, without clinical manifestations. Echocardiogram was normal. Ictal and interictal ENG-EMG, and muscle and nerve biopsies were normal. Serum potassium levels during the episodes ranged from 3 to 3.6 mEq/l (N: 3.5-4.5 mEq/l), being normal interictally (4-5 mEq/l). Oral administration of potassium did not prevent the development of episodic weakness. He had no familial history of similar symptoms. This association of periodic paralysis, cardiac arrhythmia and dysmorphic features correspond to a rare entity named Andersen's syndrome.