Dermatomyositis (DM)

Dermatomyositis(DM) is a  rare connective-tissue disease  which is an idiopathic , autoimmune and chronic inflammatory mostly involved skin and muscles. It’s  a systemic disorders  that can also  affect the joints, the oesophagus, the lungs, the kidney ,the heart ,etc. It’s more common in elderly  people (over 40 yrs).In children most often appears between 5 and 15 years. Female to male ratio is 2:1. Black more affected.

Causes:

• Idiopathic , but can be result from viral infections or cancer, that might cause autoimmune response.
• Inherited, and  HLA subtypes (HLA-DE3,HLA-DR52,HLA-DR6).
• Environmental factors
• Certain drugs like statins.
• Certain Autoimmune diseases

Risk factors:

• Genetic
• UV rays exposure(sun)
• Certain drugs eg: statins
• Environmental factors
• Viral and parasitic infections
• Epidemiological  factors

Pathophysiology:

Dermatomyositis occurs as a result of a humoral attack against the muscle capillaries and small arterioles.the disease starts when putative antibodies or other factors activate C3, forming C3b and C4b fragments that  leads to formation of C3bNEO and membrane attack complex, which  are deposited in the endomysial  vasculature.B cells and CD4 (helper) cells are also present in abundance in the inflammatory reaction associated with blood vessels.

As disease progresses , the capillaries are destroyed and the muscles undergo micro infarction. The pathogenesis of the cutaneous component of dermatomyositis  is poorly understood, but assumed as similar to muscle involvement. It’s  also by the direct cytotoxic  effect of CD8+  lymphocytes on muscles.  Others  cytokines as well as also TNF association. Abnormal T cell activity also plays  role to cause dermatomyositis.

Classification :

• Idiopathic inflammatory myopathy along with polymyositis.
• Necrotizing  autoimmune  myositis
• Cancer –associated  myositis
• Sporadic inclusion body myositis.

Sign and Symptoms:

• Symmetrical  proximal  muscles  weakness  distal  muscles preserved.
• Muscles fatigue and weakness  when climbing  stairs, walking, rising from a sitting positions, combing their hair or reaching for items  in cabinets that are above theirs shoulders.
• Muscles tenderness
• Heliotrope rash ( blue-purple) discoloration around the eyes along  with swelling, mainly  upper eyelids .
• Rash occurs  on the upper  chest or back i.e called “Shawl” (around neck)  or “V- sign” above breasts.
• Rash present on face, upper  thighs, upper  arms, or hands.
• Gottron’s  sign (scaly eruptions rash on the knuckles )
• Periungual telangiectasia
• Around 30 percent of people have swollen ,painful  but mild.
• Constitutionals  symptoms  like  fever malaise ,weakness ,fatigue,etc.
• Nail changes (capillary loop dilations) , periungual  erythema.
• “Mechanical  Hands”-rough , crackels skin at tips and lateral aspects of  the fingers resulting  in irregular ,dirty appearing lines.



shawl sign



gottron's sign

• Flagellated erythema around  front  trunk.

  

  Heliotrope rash

Others symptoms may include:

• Problem swallowing
• Lung problems
• Hard calcium deposits underneath the skin, that is mostly seen in children.
• Unintentional weight loss.

Note: ocular  muscles never Involved.

Diagnostic Criteria:

Bohans and Peter criteria –

1. Symmetric proximal muscles weakness .
2. Typical  rash (Heliotrope and  gottron’s).
3. Elevated serum muscle enzyme(CPK/aldolase).
4. Myopathic changes on EMG.
5. Characteristic muscle biopsy  abnormalities  and absence of  histopathologic signs  of other myopathies.
6. Specific test  for arthritis and arthralgia.

Diagnosis:

Lab: CBC:  Increase  inflammatory markers, anemia

Biochemical  test: CPK /aldolase (best first step in diagnosis DM) are high, C-reactive increase.

Other tests: High  result of AST (Asparted Aminotransferase) or Lactic Dehydrogenase(LDH), glutamate oxaloacetate ,pyruvate transaminase.Thyroid function test, electrolyte abnormality test( potassium,calcium,etc.), test for vitamin D 

 Clinical Urine Analysis(UA): abnormal in case of kidney affections.

Serology: + Antinuclear Antibody (ANA), Anti-Mi-2  antibodies (highly specific),Anti-Jo-1 (antihistidyl transfer RNA [tRNA].

Genetic testing: for  HLA subtypes (HLA-DR3,HLA-DR52,HLA-DR6).

Muscle biopsy( gold standard  and most accurate taste): 

Under microscope  and  finding  mononuclear  white  blood  cells ,abnormal muscles cell degeneration and regeneration, dying muscles cells .

MRI (Magnetic  resonance imaging): Guide muscle biopsy to investigate involvement of internal organs.

X-ray: Investigate joint involvement and calcifications.

Differential diagnosis:

• Polymyositis
• Polymyalgia rheumatic
• Electrolyte abnormalities ( potassium, calcium)
• Myasthenia gravis
• Eaton lambert syndrome
• Muscular dystrophy
• Infectious  myositis
• Drug induced myositis
• Inclusion boby myositis

Treatment: 

• Prednisone
• Azathioprine
• MTX
• Cyclophosphamide
• Cyclosporine
• Intravenous Immunoglobulin(IV Ig)

For skin treatment:

• Avoidance  of sun exposure and sun protections measures including broad-spectrum sunscreens.
• Hydroxychloroquine  and  Chloroquine

For  Calcinosis:

• Calcium  channel blockers i.e diltiazam(240 mg bid)  that’s help  gradual resolution of calcinosis.

Note : female patients with dermatomyositis should be screened for ovarian cancer.

Complications:

• Interstitial lung diseases
• Esophageal diseases
• Myocarditis, conductions disorders
• Trophic changes on skin (bed sores)
• Aspirated  pneumonia
• Kidney abnormalities  eg: Glomerulonephritis 
• GIT abnormalities: dyspepsia, constipation, etc
• Respiration problem  due to diaphragmatic  muscle involvement
• Malignancies

Malignancy in DM Patients:

• 48 % >65 yr.
• 9% under 65 yr.

Types of cancer: adenocarcinoma  of cervix, lung, ovaries, pancreases, bladder and stomach approx. 70% of associated  cancers.

Cancer  screening   in DM  Patients:

• Medical History and physical exam
• Age appropriate cancer screening(mammogram and colonoscopy)
• CT scan of chest, abdomen and pelvis in case of 
• increased significant risk
• Pelvic USG and transvaginal USG for female 
• Serum CA125 & CA 19-9
• PAS
• UA for blood

Prognosis :

• Spontaneous remission in 20%
• 5% have fulminant progression and eventual death
• Poor prognostic factor –recalcitrant disease, delay in diagnosis, older age, malignancy, fever, asthenia-anorexia, pulmonary interstitial fibrosis
• Causes of death- malignancy, cardiac and pulmonary dysfunction and infection.

                                                                            Image source: google image