Myotonia congenita (Thomsen’s disease) is a rare hereditary disease which occurs in autosomal dominant form and is characterized by prolonged tonic contraction and delayed relaxation of muscles which is noticeable at the beginning and end of activity.
The disease is usually observed in childhood but in many it shows up in adult life. Essential feature is prolongation of muscle contraction with slow relaxation. This is typically seen when the patient grips the hand. Myotonia manifests mainly in the lower limbs and the child finds difficulty in walking.
The body becomes rigid, the muscles are hard and prominent, and there is tendency to fall. The severity of myotonia varies. It is always increased on exposure to cold and decreased by repeated muscular activity. There may be hypertrophy of muscles and muscle strength is usually intact.
There is another form of myotonia which is autosomal recessive form and is characterized by pronounced muscle hypertrophy and muscular weakness. Myotonic dystrophy is associated with Myotonia and has other manifestations of the disease such as cataracts and muscle weakness especially of sterno mastoids and quadriceps.
Cases of myotonia congenita may have to be differentiated from myxoedema, parkinsonian rigidity and other extra- pyramidal syndromes.
Diagnosis of myotonia congenita is primarily clinical where myotonia is noticed on starting activity especially after prolonged rest. On investigations enzyme levels (SGOT, SGPT, CPK) are normal. EMG shows myotonic discharge. Muscle biopsy does not show any abnormality.
Myotonia congenita does not effect longevity. The severity of the disease decreases with advancing age. Myotonia is alleviated by use of antimyotonic agents like quinine, procainamide, phenytoin and aetazolamide.