Myasthenia gravis

Myasthenia gravis is a neurological disease which is characterized by abnormal muscle fatigability. It may affect any group of muscles; head and neck muscles are initially most affected, with extraocular muscles most commonly involved (Stell, 1987). The disease is relatively rare, with an incidence between 2 and 10 per 100 000 (Garfinkle & Kimmelman, 1982). This condition occurs in all ages, but is usually seen in young adults and is twice as common in women as men. Onset for females is reported in the third decade of life, while in males it is during the sixth decade (Garfinkle & Kimmelman, 1982). Aetiology is unknown, but current evidence suggests that it is an autoimmune disease attributed to a decrease in the number of acetylcholine receptors in the motor end plate (Fritze et al., 1974).

Patients with myasthenia gravis tend to show bulbar symptoms, with the initial and most common being drooping of the eyelids or ptosis (Grob, 1961). They also report dysarthria characterized by hypernasality, reduced loudness, increased breathiness and articulatory imprecision (Aronson, 1990), dysphagia, diplopia, weakness of the legs and blurred vision. The unique features of myasthenia gravis are fatigability, fluctuation of function and restoration of function after rest (Colton & Casper, 1990). Diagnosis depends on the typical clinical picture and can be confirmed by intravenous administration of edrophonium (Tensilon Test), laryngeal electromyographic measurements or detection of anti-acetylcholine receptor antibodies in the blood.