Myositis

Myositides are inflammatory diseases of the muscles and are also referred to as inflammatory myopathies. They arise idiopathically ((most often)), or infectiously by direct attack of the muscle by the causative agent. Inflammatory changes in muscle tissue can also be accompanied by systemic diseases (eg. vaskulitis). Idiopathic myositis is characterized by a chronic course with an autoimmune origin, and the histological image from a biopsy plays an important role in their diagnosis.

Idiopathic myositis

Skin involvement in dermatomyositis

Within the framework of idiopathic, non-infectious myositis, we distinguish three diseases that most often appear around the age of 40 and their incidence increases with age:

• Polymyositis – the main symptom is weakness of proximal muscle groups and the histological picture is dominated by a CD8+ lymphocytic infiltrate invading even intact muscle fibers
• Dermatomyositis – similar symptoms to polymyositis with skin changes typically in small joints and nails, also occurs paraneoplastically and has specific perifascicular atrophy with CD4+ infiltrates
• Myositis with inclusion bodies – characteristic proximal and distal muscle weakness with specific fibrous inclusions observable mainly in an electron microscope

Corticosteroids (e.g. prednisone ) are used in therapy (prednison), but IBM usually does not respond to treatment. They are sometimes also called autoimmune mysoitis.

Infectious myositis

They have a known cause and arise together with an infectious disease or direct entry of an infectious agent, e.g. during traumatic muscle damage. They are divided according to the originator and the most common include:

• Viral – coxsackie B viruses; CMV; AIDS (HIV myositis).
• Bacterial – clostridie (gaseous sputum); secondary infection of bedsores a necrosis; when TB, spreads , e.g. from bones.
• Parasitic – in Trichinellosis, or cysticerkosis (often asymptomatic).

General clinical aspects

It is good to suspect myositis when:

1. Myalgias and muscle weakness.
2. Rapid onset of symptoms and progression within a few weeks.
3. Alternating course of the disease with remissions.
4. Palpation findings without pseudohypertrophy.
5. The presence of skin changes.
6. Comorbidities (tumor and autoimmune diseases).

Links

related articles

• Neuromuscular diseases (signpost)
• Myopathy

References

• KRAHMS, Matthias. Kurzlehrbuch Pathology. 2nd edition. Stuttgart. 2013. pp. 476-478.