Diagnosis

Diagnosis of this rare condition is sometimes delayed, since early symptoms of mild muscle weakness and fatigability are variable and difficult to demonstrate on clinical examination.

In suspected cases an injection of a drug called edrophonium (Tensilon) in the hospital clinic can be used to confirm the diagnosis. This drug causes a temporary enhancement of the amount of acetylcholine, the chemical transmitter, at the neuromuscular junction. This leads to immediate, but short lived, improvement in the muscle power of the affected muscles. For example the drooping of the eyelids and double vision in ocular myasthenia improves temporarily following injection. Further investigations are also undertaken including blood tests for anti-acetyl choline receptor antibodies, other abnormal antibodies and electrophysiological tests of nerves and muscles. X-rays, MRI and CT scans of the chest are obtained to detect enlargement of the thymus or presence of a tumour.

Amended June 2008