Muscle Disease and Myasthenia Gravis

Muscle pain, cramps, spasms & stiffness and movements (fasciculations) are usually benign. Polymyalgia rheumatica & fibromyalgia occupy a difficult space between the specialities of neurology and rheumatology. Other important causes of muscle disease not mentioned include endocrine (thyroid-associated), drug-induced and toxic (alcohol) causes. The Lambert-Eaton myasthenic & the Stiff-Man syndromes should be researched.

1. Muscle Disease

Muscle diseases, or myopathies tend to produce more weakness around the hip and shoulder girdles than in the hands and feet. Presenting features include difficulty in raising the arms above head level, hair washing and getting out of a car or low chair or sofa. There are also problems in going up stairs without pulling up on the bannisters.

With respect to cause, age at symptom onset is significant, and probing of developmental history eg sporting achievements at school, is important. Many myopathies run in families and some may result from exposure to drugs and poisons.

Myopathies may broadly be divided into three main categories. Firstly, there are the muscle dystrophies where muscle fibres simply degenerate or have failed to develop properly, and there are very few useful treatments. Secondly, there are the metabolic myopathies in which there is a disorder of muscle biochemistry. Lastly, there is a group of inflammatory myopathies where steroids and immunosuppressant treatments may have a role.

Testing involves bloods, neurophysiology, MR Imaging and muscle biopsy.

2. Myasthenia Gravis

This is a rare acquired disease of the neuromuscular junction, the place where the nerve meets the muscle, in which there is destruction of muscle receptors by one's own antibodies in an "autoimmune" attack.

The crucial presenting feature is muscle weakness which is fatigueable and helped by rest. Presenting symptoms include double vision, eyelid drooping or "ptosis", problems with speech, chewing and swallowing, limb muscle weakness and breathlessness.

Investigation includes the use of the Tensilon test in which the levels of nature's own neurotransmitter are artificially boosted just for a few minutes in an effort to overcome the receptor deficiency. Neurophysiology and serum assay of the responsible antibody are additional tests. Occasionally, myasthenia is associated with a tumour of the thymus gland which lies in the front of the chest and imaging studies either with CT or MR should be carried out to exclude this. Myasthenia is often associated with other autoimmune disease including diabetes mellitus, thyroid disease, rheumatoid arthritis and pernicious anaemia and simple blood tests may reveal these.