Muscle
Muscle
Dermatomyositis

Author: Meggen A. Walsh, M.D. (see Authors page)
Editor: Jesse Kresak, M.D.

Revised: 9 May 2016, last major update April 2016

Copyright: (c) 2003-2016, PathologyOutlines.com, Inc.

PubMed Search: Muscle dermatomyositis[title]
Cite this page: Dermatomyositis. PathologyOutlines.com website. http://pathologyoutlines.com/topic/muscledermatomyositis.html. Accessed August 18th, 2017.
Definition / general
  • Idiopathic process that leads to an inflammatory myopathy with skin manifestations
Essential features
  • Myositis with perifascicular muscle fiber atrophy and generally inflammatory infiltrates around intramuscular vessels
  • Clinical history can be supportive, with the classic skin finding being a heliotrope rash of the eyelids, face, neck and MCP joints
Terminology
  • Dermatomyositis, DM
  • Dermatomyositis sine myositis or amyopathic myositis: without muscle involvement
  • Dermatomyositis sine dermatitis: either no skin findings or skin findings not noted in darker skin individuals:
Epidemiology
  • There are two forms, adult and juvenile
  • Adult dermatomyositis peaks ~ age 50; twice as common in women than men
  • Juvenile dermatomyositis tends to occur between 5-10 years
  • Dermatomyositis is the most common form of inflammatory myopathy in children (as opposed to polymyositis and inclusion body myositis)
Sites
  • Symmetric weakness that affects the proximal limb muscles
  • This weakness is progressive and occurs over weeks to months
  • There are rare acute cases of weakness
  • Patients describe difficulty rising from a seated position or chair, lifting objects or climbing stairs
  • Distal weakness, in general, is not a presenting symptom
Pathophysiology
  • The primary process is attack on the endothelium of the capillaries of myofibers, with deposition of complement on the vessel walls and eventual formation of membrane attack complex (N Engl J Med 1986;314:329)
  • This causes perivascular inflammation and can eventually reduce the number of intramuscular small vessels
  • This causes hypoxic change in the muscle, characterized by perifascicular atrophy, since these fibers are more distal to the vessels (N Engl J Med 1991;325:1487)
  • In chronic disease, the number of capillaries can be significantly reduced in a biopsy
  • There is up regulation of MHC-1 in myofibers and also increased expression of ICAM1 (N Engl J Med 1993;329:1993)
  • No viral etiology has been associated with dermatomyositis
Etiology
Clinical features
  • The classic symptoms are a rash followed by mild to severe myopathy
    • Some cases have no rash or an unrecognized rash in darker skinned individuals (dermatomyositis sine dermatitis)
    • Some cases lack muscle involvement (dermatomyositis sine myositis or amyopathic myositis)
  • The skin rash is helicotrophic (violaceous, purple-blue) with edema over the upper eyelids; it can also involve the face, neck, anterior chest, back, shoulders, elbow and knees
  • The rash is called the "V sign" when it occurs on the chest, and the "shawl sign" when it occurs on the back / shoulders (N Engl J Med 1991;325:1487)
  • Classic findings also include Gottron's papules (elevated, purple rash on MCP joints), dilated capillaries at the base of the nails, skin calcinosis in chronic cases and a tiptoe gait from contractures in children when chronic (N Engl J Med 1991;325:1487)
  • Occasionally patients have idiopathic interstitial lung disease (Clin Rheumatol 2007;26:1647)
Clinical images

Images hosted on other servers:

Heliotrope rash: the "classic" violaceous
rash over the eyes and the malar
region of the face

Gottron's papules: erythematous papules on the dorsum
of MCP or interphalangeal joints; biopsy shows
acanthosis and hyperkeratosis with vacuolar change
and a scattered perivascular inflammatory infiltrate


Calcinosis: subcutaneous cases occur in long term,
intractable cases, usually of juvenile type

Diagnosis
  • A clinical-pathologic diagnosis
  • Skin and muscle biopsies can be performed at the same time, although a clinical history of skin rash may override the need for a skin biopsy
  • EMG/NCS [nerve conduction studies] findings may show increased membrane irritability (Up To Date)
Laboratory
Radiology description
Prognostic factors
  • Response to therapy and presence of an underlying malignancy are useful factors
Case reports
Treatment
Gross description
  • The skeletal muscle gross findings are non-specific
Microscopic (histologic) description
  • Perifascicular atrophy is the hallmark of dermatomyositis
  • Muscle may have altered muscle fiber sizes, but there is less of a tendency to hypertrophy muscle fibers (more common in dystrophy)
  • May be increased internal nuclei and basophilic myofibers
Microscopic (histologic) images

Images hosted on Pathout server - Contributed by Drs. Meggen A. Walsh and Jesse Kresak:

Perifascicular atrophy (H&E, ? stain, GMS, right 2 images are myosin I/II immunostain)

Cytology description
  • Cytology is of no benefit since the main feature is atrophy in the perifascicular region
Positive stains
  • Biopsy shows increased CD4+ T cells
  • H&E cross sections are best to examine perifascicular atrophy
Negative stains
  • Dystrophy panel is normal
  • No loss of enzyme histochemical stains
Electron microscopy description
  • Intramuscular vessels will occasionally show tubuloreticular inclusions
Differential diagnosis
  • Myasthenia gravis: also causes muscle weakness, but has ophthalmologic muscular fatigue (DM does not)
  • Polymyositis: Similar inflammatory myopathy, but no prominent perifascicular atrophy