Authors:
Helly Hammer (Bern | CH)
Claudia Maurer (Bern | CH)
Nicole Kamber (Bern | CH)
Anelia Dietmann (Bern | CH)
Olivier Scheidegger (Bern | CH)
H. Hammer, C. Maurer, N. Kamber, A. Dietmann, O. Scheidegger
1Department of Neurology, Inselspital Bern, University Hospital, University Bern, Switzerland
Case Report and Video
Differential diagnosis of myotonia: Is temperature the key?
A man in his early 30s complains since the early adolescence about muscle stiffness of his legs, which spread over the years also onto his arms and face and which increases with warmth and decreases when exposed to the cold.
The clinical findings showed a slight distal tetraparesis with myotonic reaction with prolonged muscle relaxation while opening the fist or opening the eyes, slight Facies myopathica with ptosis, bald forehead, and high arched palate). However, percussion myotonia was not detected.
Due to the clinical presentation, a needle electromyography was preformed, which showed myotonic discharges. The initial hypothesis was primarily a myotonic dystrophy type 1 (Curshmann Steinert) or typ II (PROMM). A genetic test for MD type I and II was initiated and returned negative.
Therefore, more electrophysiological testing was performed, including a “short exercise and cold test”: recording electrodes where placed on right M. abductor digiti minimi (ADM) with stimulation of the right N. ulnaris at the wrist. The first stimulation was done at room temperature for a baseline of the compound muscle action potential (CMAP). Afterwards the hand was cooled with cold packs for 10 minutes and the patient was asked to do an isometric contraction of the ADM for 15 seconds for 3 times with afterwards measurement of the CMAP every 15 seconds during one minute. After cooling, a reduction of the CMAP was found, improving with each trial of muscle exercise, corresponding to an electrodiagnostic Pattern II as described by Fournier et al. 2004 for ion channel myotonia.
Genetic testing confirmed a mutation in the CLCN1 gene, encoding for the chloride channel, resulting in congenital myotonia.