A Multisystem Muscle Disorder Needs Monitoring

Fig. 36.1

Tongue myotonia following percussion

Investigations

Her CK was normal. EMG demonstrated frequent myotonic potentials with mild myopathic changes. An overnight sleep study showed significant desaturations throughout the night, with the lowest oxygen saturation dropping to 72 % with an average of 85 %. An expansion of the CTG repeat at the 3’ end of myotonic dystrophy protein kinase (DMPK) gene was confirmed.

Diagnosis

Myotonic Dystrophy Type 1.

Discussion

The patient developed late-onset myotonia with a typical pattern of weakness, neuromuscular respiratory failure and cardiac dysrhythmias. This suggested a multisystem myotonic disorder suggestive of a myotonic dystrophy. The non-dystrophic myotonias tend to begin in childhood and do not cause multi-system disease. Myotonic dystrophy type 2 tends to be less severe and less common than type 1.

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