66 Myasthenia gravis
Instruction
This patient complains of drooping of the eyelids in the evenings; examine this patient.
Salient features
History
• Weakness in muscles is more marked in the evening
• Muscle weakness which increases with exercise (remember that fatigability is the hallmark of myasthenia gravis) and is painless
• Muscle weakness affects smiling (Fig. 66.1), chewing, speaking, muscles of the neck, walking, breathing, movements at the elbow and hand movements
• Obtain history of thyrotoxicosis, diabetes mellitus, rheumatoid arthritis, SLE and thymoma
• Ask about d-pencillamine treatment for rheumatoid arthritis (myasthenia gravis is sometimes caused by d-pencillamine).
Examination
• The patient may have obvious ptosis
• Check for worsening of ptosis after sustained upward gaze for at least 45 s
• Check extraocular movements for diplopia and variable squint
• Comment on snarling face when the patient attempts to smile
• Weakness without loss of reflexes or alteration of sensation or coordination. The weakness may be generalized; it may affect the limb muscles, often proximal in distribution, as well as the diaphragm and neck extensors
• Muscle wasting is rare and when present inidicates it is late in the disease
