Polymyositis

What it is

A rare idiopathic inflammatory myopathy (IIM) historically characterized by symmetric proximal muscle weakness, elevated muscle enzymes (creatine kinase), myopathic findings on electromyography, and muscle biopsy showing endomyial infiltration composed mainly of macrophages and lymphocytes. The features are non-specific, thus the disease should be distinguished from similar entities with specific clinical, immunological, histological features, notably dermatomyositis, immune-mediated necrotizing myopathy, anti-synthetase syndrome, inclusion body myositis, and myositis associated with other connective tissue disorder.

Key facts

Prevalence

1-9 / 100 000 (Europe)

Age of onset

Adult, Elderly

Inheritance

Not applicable

Classified as

Disease

Prevalence figures describe populations, not individuals, and are often estimates from a single study. Where the figure is an incidence or a birth prevalence, it says so.

Signs and symptoms

These ranges are how often a sign appears across everyone diagnosed, not a prediction for one person — most people have some of these and not others. Orphanet also records findings that are specifically absent in this disease; those are in the data but not listed here.

ICD-10 codes

ICD-10 has no distinct code for most rare diseases, so many are filed under the nearest available one. A shared code identifies the group, not this disease — the ORPHAcode above is what identifies it.

Related health topics

Reached through the ICD-10 categories this disease is filed under, so these describe the broader group rather than this disease specifically.

Cross-references