Polymyositis

Polymyositis is an autoimmune inflammatory myopathy in which CD8+ cytotoxic T cells and macrophages invade the endomysium and damage muscle fibres. Necrosis allows intracellular CK to leak into the blood. The result is usually gradual, symmetric weakness of muscles closest to the trunk: the hips, thighs, shoulders, upper arms, and sometimes the neck. The patient may describe difficulty rising from a chair, climbing stairs, lifting the arms to wash or brush the hair, or keeping the head upright. Sensation is generally preserved, which helps distinguish a primary muscle disorder from many peripheral neuropathies. A prominent rash should prompt consideration of dermatomyositis rather than classic polymyositis. Swallowing and breathing can be affected because the pharyngeal and respiratory muscles are skeletal muscle too. Dysphagia is therefore not simply a comfort complaint; retained food or secretions can enter the airway. Interstitial lung disease (ILD) is particularly important when myositis occurs with anti-Jo-1 or another antisynthetase antibody. Antisynthetase syndrome may include myositis, ILD, arthritis, Raynaud phenomenon, fever, and mechanic’s hands. The term polymyositis now describes a relatively uncommon diagnosis. Many patients once given this...