Family history for early onset cataracts, frontal balding, diabetes, neuromuscular disorders, and cognitive impairment is helpful in establishing a diagnosis in this autosomal dominant disorder. Myotonia should only occur with voluntary contraction of muscle. Stiff person syndrome involves the abdominal muscles and is frequently associated with diabetes mellitus. Individuals with stiff person syndrome tend to have a marked startle response and the spasms disappear in sleep. Furthermore, neuromyotonia is a failure to relax following muscle contraction, and contractions persist during sleep.
Benign fasciculations are a diagnosis of exclusion.
The lack of muscle cramps or weakness makes a diagnosis of myopathy unlikely, and a 7-year history of muscle twitching without associated weakness would be highly unusual for motor neuron disease. A primary movement disorder, including some form of tremor or dystonia, should be considered, although involvement of the abdominal muscles is highly atypical for either of these problems. Encephalomyelitis is occasionally associated with rigidity. The history of progression would lean against the possibility of a toxic etiology. Alcohol ingestion should be excluded by the history, assuming its accuracy.