DEAR DR. DONOHUE: My mother was recently struck down by what her doctor says is polymyositis. I had to take her to the emergency room, and they kept her in the hospital for five days. She was released to a convalescent center. She has regained some strength in her arms, but her lower half remains weak. Could you shed some light on polymyositis? – G.B.Y.

ANSWER: Polymyositis (POL-ee-MY-oh-SITE-iss) is a somewhat uncommon illness where many (the “poly” of polymyositis) muscles (the “myo” of polymyositis) are inflamed (the “itis” of polymyositis). It can strike at any age, but there are two age peaks for it. One occurs between the ages of 7 and 15, and the other between 30 and 50.

The cause has eluded discovery, but there is strong evidence that the immune system is inappropriately involved in an assault on muscles. Genes are also implicated, and most likely some environmental trigger plays a role.

Usually the illness creeps up on a person gradually. Muscle weakness is the hallmark symptom, and the weakness can become so profound that people cannot rise from a chair, climb stairs or reach up to their head to comb their hair.

The physical symptoms strongly suggest the illness. Finding strange antibodies – the work of the immune system – in the blood adds more evidence for the diagnosis.

Prednisone, one of the cortisone drugs, is the medicine most often used in treating this disease. Cortisone drugs are the most powerful anti-inflammatory medicines available. Sometimes additional medicines that have a direct effect on the immune system are added.