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Dermatomyositis
Classification & external resources

X-Ray of the knee in a patient with dermatomyositis.
ICD-10	M33.0-M33.1
ICD-9	710.3
DiseasesDB	10343
MedlinePlus	000839
eMedicine	med/2608  derm/98
MeSH	D003882

Dermatomyositis is connective-tissue disease that is characterized by inflammation of the muscles and the skin. Its cause is unknown, but it may result from either a viral infection or an autoimmune reaction. Up to 50% of the cases may be a paraneoplastic phenomenon, indicating the presence of cancer.

X-ray findings include dystrophic calcifications in the muscles.

There is a form of this disorder that strikes children, known as juvenile dermatomyositis.

"Gottron's papules", pink patches on the knuckles, and priapism, are associated with this disorder.

Contents 1 Classification 2 Signs and symptoms 3 Pathology 4 Microscopic findings 5 Mechanism 6 Differential diagnosis 7 Treatment 8 References 9 External links

Dermatomyositis is a type of autoimmune connective tissue disease. It is related to polymyositis and inclusion body myositis.

The main symptoms include skin rash and muscle pain. Characteristic signs include a heliotrope rash (a purple/red rash affecting the eyelids, cheeks, forehead and nasolabial folds) and Gottron's papules (purple/red raised plaques over the knuckles and extensor regions).

The diagnosis of dermatomyositis can be confirmed by muscle biopsy. There are two classic microscopic findings of dermatomyositis. They are:

• A mixed B- and T-cell perivascular inflammatory infiltrate
• Perifascicular muscle fiber atrophy

Dermatomyositis is associated with autoantibodies, especially anti-Jo-1 antibody.^[1]

Cross sections of muscle reveal muscle fascicles with small, shrunken polygonal muscle fibers on the periphery of a fascicle surrounding central muscle fibers of normal, uniform size.

Aggregates of mature lymphocytes with small, dark nuclei and scant cytoplasm are seen surrounding vessels. Other inflammatory cells are distinctly uncommon. Immunohistochemistry can be used to demonstrate that both B- and T-cells are present in approximately equal numbers.

The mechanism is conjectured to be complement-mediated damage of microscopic vessels with muscle atrophy and lymphocytic inflammation secondary to tissue ischemia.^[2]

Dermatomyositis must be differentiated from other common, lymphocyte predominant inflammatory myopathies. If present, the characteristic perifascicular atrophy makes this distinction trivial.

There is some overlap in the microscopic appearances of different inflammatory myopathies, but some helpful differences are often present.^[3] The rimmed vacuoles of inclusion body myositis (IBM) are absent in dermatomyositis. Polymyositis is characterised by diffuse or patchy inflammation of the muscle fascicles, a random pattern of muscle atrophy, and T-cell predominance with T-cells seen invading otherwise viable appearing muscle fibers.^[1]

1. Prednisolone
2. Intravenous immunoglobulin
3. Azathioprine
4. Cyclophosphamide

1. ^ Ghirardello, A; Zampieri S, Tarricone E et al. (May 2006). "Clinical implications of autoantibody screening in patients with autoimmune myositis". Autoimmunity 39 (3): 217-221. PMID 16769655. 
2. ^ Benveniste, O; Squier W, Boyer O et al. (Nov 2004). "Pathogenesis of primary inflammatory myopathies". Presse Médicale 33 (20): 1444-1450. PMID 15611679. 
3. ^ Nirmalananthan, N; Holton JL, Hanna MG (Nov 2004). "Is it really myositis? A consideration of the differential diagnosis". Current Opinion in Rheumatology 16 (6): 684-691. PMID 15577605. 

• The American College of Rheumatology's patient education page on myopathy
• Illustration of Gottron's papules

v • d • e Muscular Dystrophy
The Nine Primary Muscular Dystrophies	Becker's • Congenital • Duchenne • Distal • Emery-Dreifuss • Facioscapulohumeral • Limb-girdle muscular dystrophy • Myotonic • Oculopharyngeal
Related topics
National/International Organizations	Muscular Dystrophy Association (USA) . Muscular Dystrophy Canada
US government Institutes and Legislation	NINDS • NIAMS • NICHD • MD CARE Act • Genetic Information Nondiscrimination Act • Americans with Disabilities Act of 1990
National/International Events	Jerry Lewis MDA Telethon (USA)
Recent or Ongoing Clinical Trials	Stamulumab (MYO-029)

v • d • e Diseases of the musculoskeletal system and connective tissue (M, 710-739)
Arthropathies	Arthritis (Septic arthritis, Reactive arthritis, Rheumatoid arthritis, Psoriatic arthritis, Felty's syndrome, Juvenile idiopathic arthritis, Still's disease) - crystal (Gout, Chondrocalcinosis) - Osteoarthritis (Heberden's node, Bouchard's nodes) acquired deformities of fingers and toes (Boutonniere deformity, Bunion, Hallux rigidus, Hallux varus, Hammer toe) - other acquired deformities of limbs (Valgus deformity, Varus deformity, Wrist drop, Foot drop, Flat feet, Club foot, Unequal leg length, Winged scapula) patella (Luxating patella, Chondromalacia patellae) Protrusio acetabuli - Hemarthrosis - Arthralgia - Osteophyte
Systemic connective tissue disorders	Polyarteritis nodosa - Churg-Strauss syndrome - Kawasaki disease - Hypersensitivity vasculitis - Goodpasture's syndrome - Wegener's granulomatosis - Arteritis (Takayasu's arteritis, Temporal arteritis) - Microscopic polyangiitis - Systemic lupus erythematosus (Drug-induced) - Dermatomyositis (Juvenile dermatomyositis) - Polymyositis - Scleroderma - Sjögren's syndrome - Behçet's disease - Polymyalgia rheumatica - Eosinophilic fasciitis - Hypermobility
Dorsopathies	Kyphosis - Lordosis - Scoliosis - Scheuermann's disease - Spondylolysis - Torticollis - Spondylolisthesis - Spondylopathies (Ankylosing spondylitis, Spondylosis, Spinal stenosis) - Schmorl's nodes - Degenerative disc disease - Coccydynia - Back pain (Radiculopathy, Sciatica, Low back pain)
Soft tissue disorders	muscle: Myositis - Myositis ossificans (Fibrodysplasia ossificans progressiva) synovium and tendon: Synovitis - Tenosynovitis (Stenosing tenosynovitis, Trigger finger, DeQuervain's syndrome) bursitis (Olecranon, Prepatellar, Trochanteric) fibroblastic (Dupuytren's contracture, Plantar fasciitis, Nodular fasciitis, Necrotizing fasciitis, Fasciitis, Fibromatosis) enthesopathies (Iliotibial band syndrome, Achilles tendinitis, Golfer's elbow, Tennis elbow, Metatarsalgia, Bone spur, Tendinitis) other, NEC: Muscle weakness - Rheumatism - Myalgia - Neuralgia - Neuritis - Panniculitis - Fibromyalgia
Osteopathies	disorders of bone density and structure: Osteoporosis - Osteomalacia - continuity of bone (Pseudarthrosis, Stress fracture) - Monostotic fibrous dysplasia - Skeletal fluorosis - Aneurysmal bone cyst - Hyperostosis - Osteosclerosis Osteomyelitis - Avascular necrosis - Paget's disease of bone - Algoneurodystrophy - Osteolysis - Infantile cortical hyperostosis
Chondropathies	Juvenile osteochondrosis (Legg-Calvé-Perthes syndrome, Osgood-Schlatter disease, Köhler disease, Sever's disease) - Osteochondritis - Tietze's syndrome
See also congenital conditions (Q65-Q79, 754-756)