by Dr John Rees
Diseases of muscles (myopathies) is this month’s topic for discussion with Dr John Rees in his neurological health series.
We have all heard of muscle disease affecting young boys on a familial basis, but this is only a very small part of the wide spectrum of diseases causing muscle weakness. The muscular dystrophies include Duchenne, Becker, Facioscapulohumeral, Scapuloperoneal, Oculopharangeal and Limb girdle types. It can be seen that these are named initially after the physician who first described the syndrome and then a more descriptive title that indicates the different muscle groups that are involved. These diseases develop at different ages, may be gender based, are genetically based, distinct and have varying degrees of severity, some of which shorten life.
The congenital group (present at birth), include, myotonic dystrophy, myotonia congenita and paramyotonia congenita. Congenital hypotonia, Central core disease and Prader Willi syndrome do not have myotonia which is a condition where the muscle is unable to relax normally.
Some disorders of the body’s metabolism can cause muscle weakness e.g. abnormal levels of sodium, potassium and calcium, deficiencies of certain enzymes e.g. myophosphorylase. Also, disorders of the mitochondria, which are passed on only by the mother e.g. Kearns Sayer syndrome, MELAS and others.
There are a range of muscle disorders occurring in the context of inflammation of muscles, usually on an auto immune basis often in association with other auto immune conditions, sometimes with a cancer. Occasionally a virus can cause direct muscle damage.
The key to recognising a myopathy is to understand that the patient’s symptoms and abnormalities when examined are due to weakness primarily of the hip and shoulder girdle muscles. Other diseases that can secondarily affect muscles will have a different distribution of weakness and so ‘pattern recognition’ is very important. The various groups that have been mentioned often have subtle differences of emphasis that allow the experienced clinician in association with the history to recognise which of the many possibilities is most likely.
Diagnosis is aided by electrical interrogation of the muscles (electromyography), detecting an enzyme called creatine phosphokinase that leaks out of damaged muscle cells into the blood stream, checking the various constituent blood chemicals and if necessary, looking at the various endocrine and metabolic conditions that may be at fault. Detailed analysis of a muscle biopsy is often an essential step in diagnosis. These days, very sophisticated genetic analysis allows the categorisation of many conditions that were not understood some years ago. This has led to the identification of abnormal or missing enzymes and/or chemical pathways that offer the potential for treatment and even cure if genetic engineering can be utilised. There have been enormous strides in our understanding of muscle diseases in recent years and the head of the internationally renowned Newcastle Muscle unit was recently awarded a knighthood in recognition of their achievements.
Many of these conditions are serious at presentation or can become so, even life threatening, if breathing muscles are involved. Some conditions are associated with damage to heart muscle with obvious implications and some react badly to anaesthetics. Many are associated with a shortened life span. It is important therefore to identify, quickly if possible, the exact nature of the myopathy and to institute the appropriate treatment (often steroids and/or anti-cancer drugs), if indeed there is one.
Diagnosis and follow up by a neurological muscle expert, which will include detailed physio and occupational therapy is essential. Muscle disease can impact work, family and social life but help is available from places such as Muscular Dystrophy UK and the Brain & Spine Foundation.