Inflammatory myopathies: Clinical

Inflammatory myopathies refers to a group of three disorders - polymyositis, dermatomyositis, and inclusion body myositis.

They’re all autoimmune disorders that cause muscle inflammation, leading to progressive muscle weakness and wasting.

Sometimes, the muscles can be tender or painful. In severe cases, it can involve the respiratory muscles, which can be life threatening.

Usually, there’s also systemic symptoms like fever, fatigue, and weight loss; as well as other organ-specific symptoms.

There can be subcutaneous calcification in the skin; joint pain and arthritis; cardiovascular conditions like arrhythmias, myocarditis, and pericarditis; gastrointestinal conditions like gastroesophageal reflux disease and dysphagia; respiratory problems like aspiration pneumonia; and vascular problems like Raynaud’s phenomenon, where arterial spasm causes reduced blood flow to the fingers.

Let’s start off with polymyositis, which typically affects adults, and it’s characterized by bilateral muscle weakness that mostly affects proximal, large muscle groups, like the shoulder or hips and spares the distal muscles like muscles in the hands.

Individuals might have difficulty rising from a chair, lifting their arms, or climbing stairs.

The muscle weakness usually worsens gradually over several months, and over time there can be muscle atrophy.

Dermatomyositis has the same muscular presentation as polymyositis, but it mainly affects children, and in addition to muscle weakness, children can have a skin rash.

One type of rash is the heliotrope or lilac rash, which is a pruritic purplish rash that can appear on or around the eyelids.

A similar rash may appear on sun-exposed areas, like the chest, shoulders, or thighs.

This rash is similar to the malar rash of individuals with lupus, but it typically extends beyond the nasolabial folds, which is a region that’s usually spared in lupus.