[1] Diagnosis is typically based on some combination of symptoms, blood tests, electromyography, and muscle biopsies.

[7] The main symptoms include several kinds of skin rash along with muscle weakness in both upper arms or thighs.

[12] Tasks that use these muscles: standing from sitting, lifting, and climbing stairs, can become increasingly difficult for people with dermatomyositis.

This causes difficulty breathing, and dermatomyositis is considered to be a restrictive lung disease in patients with these symptoms.

[15] Later in the course of the disease, patients often experience difficulty swallowing, called dysphagia, which makes it hard to move food from the mouth to the stomach.

The muscles of the esophagus may become weak, leading to reduced or irregular movements that prevent proper swallowing.

Additionally, individuals might suffer from gastroesophageal reflux disease (GERD), where stomach acid flows back into the esophagus, causing heartburn and irritation.

[3] The pathogenesis of dermatomyositis involves an autoimmune-mediated process characterized by immune complex deposition and complement activation, leading to microangiopathy in both muscle and skin tissues.

[16] The microangiopathy has a non-uniform pattern: within a single muscle fiber, some capillaries may be heavily affected while others seem to be unharmed.

[17] The complement system plays a crucial role in the tissue injury of dermatomyositis, through the formation and deposition of immune complexes.

Autoantibodies target muscle and skin antigens, leading to the activation of the classical complement pathway, ultimately forming the membrane attack complex (MAC) on the endothelial cells of microvasculature.

However, the specific sequence of complement activation is not completely understood and may depend on the pathological subtype of the disease.

[3] Inherited genetic factors play at least a partial role in developing the disease, and HLA subtypes HLA-DR3, HLA-DR52, and HLA-DR6 seem to create a disposition to autoimmune dermatomyositis.

[10] Dermatomyositis is a form of systemic connective tissue disorder, a class of diseases that often involves autoimmune dysfunction.

Other immunosuppressive agents used to treat the inflammation associated with dermatomyositis include cyclosporine A, cyclophosphamide, and tacrolimus.

Surgery may be required to remove calcium deposits that cause nerve pain and recurrent infections.

[28][29] As of 2016, treatments for amyopathic dermatomyositis in adults did not have a strong evidence base; published treatments included antimalarial medications, steroids, taken or orally or applied to the skin, calcineurin inhibitors applied to the skin, dapsone, intravenous immunoglobulin, methotrexate, azathioprine, and mycophenolate mofetil.

[24][27] Before the advent of modern treatments such as prednisone, intravenous immunoglobulin, plasmapheresis, chemotherapies, and other drugs, the prognosis was poor.