Dermatomyositis

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**Dermatomyositis**
*Classifications and external resources*
ICD-10	M33.0-M33.1
ICD-9	710.3
DiseasesDB	10343
MedlinePlus	000839
eMedicine	med/2608 derm/98

X-Ray of the knee in a patient with dermatomyositis.

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, are associated with this disorder.

[edit] Pathology

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

Microscopic findings

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.

Mechanism

The mechanism is conjectured to be complement-mediated damage of microscopic vessels with muscle atrophy and lymphocytic inflammation secondary to tissue ischemia ^[1].

Differential Diagnosis

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.^[2] 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.^[3]

Signs: Periorbital Heliotrope Rash (HELIOTROPE RASH: purple /erythematous rash affecting eyelids, malar, forehead and nasolabial folds), Gottrun papules at the knuckles(Purple /erythematous raised lesions over knuckles and extensor regions).

Treatment

1. High Dose Prednisolone 2. Methotrexate (complication: may cause Interstitial Lung Disease) 3. IVIG

[edit] References

↑ Benveniste O, Squier W, Boyer O, Hilton-Jones D, Herson S. Presse Med. 2004 Nov 20;33(20):1444-50. PMID: 15611679
↑ Nirmalananthan N, Holton JL, Hanna MG. Is it really myositis? A consideration of the differential diagnosis. Curr Opin Rheumatol. 2004 Nov;16(6):684-91.