Dermatomyositis and Polymyositis- Idiopathic Inflammatory Myopathies

-Present with PROXIMAL muscle weakness (eg: difficulty climbing stairs, getting up from chair)
-Evidence of muscle inflammation (Elevated CK, Aldolase but also includes elevated LDH, AST, ALT)
–Skin manifestations (Dermatomyositis)

Problem Representation for Dermatomyositis (see exception below)

-Usually female (2:1 Female:Male involvement) at any stage of life but peak incidence age 40-50, who presents with gradual onset (weeks-months) of symptoms

Making the diagnosis of Dermatomyositis

-Ask about proximal weakness
-Ask about cutaneous eruptions (see below)
-Ask about systemic involvement (dysphagia from oropharyngeal or esophageal muscle involvement or dyspnea from ILD)
-Rule out drug myopathy (Glucocorticoids, Statins, Fibrates, Alcohol, Anti-Malarial drugs, Colchicine but LONG list of drugs that can cause myopathy

(+) autoantibodies in 80 % of patients with DM and PM (ANA/Anti-Jo-1/Anti-SRP/Anti Mi-2 among others)

Clinical presentation and physical exam

-90 % of patients will have muscle weakness (proximal and symmetric)
-Pain and stiffness are NOT prominent and only about 50 % of patients will have myalgias and muscle tenderness
–Crackles on exam (if ILD is present)

Skin manifestations (pictures from UptoDate)

Heliotrope Rash

Cuticular overgrowth, periungal erythema, dilated capillary loops

Erythematous to violaceous patches with overlying scale are present on the extensor surfaces

Mechanic’s Hands (note the thickening)

Holster Sign (on lateral thigh)

Shawl Sign (on back), V sign can be seen on front

Gottron’s Papules

Anti-Synthetase Syndrome (~30 % of patients with DM/PM

–ACUTE onset (different than usual sub-acute presentation) + constitutional symptoms + myositis + Raynaud + non-erosive arthritis + mechanic’s hands (see picture above) and positive anti-synthetase antibody (Anti-Jo)
-Important to recognize due to higher risk of developing Interstitial Lung Disease (ILD)

Testing

EMG

-Can support diagnosis of inflammatory myopathy but not diagnostic for PM or DM and can see similar findings in viral, infectious, toxic, or metabolic myopathies

Muscle Biopsy

–Can distinguish DM, PM, and inclusion body myositis

Association with Malignancy

DM and PM (DM>PM) puts you at HIGHER risk for adenocarcinoma malignancy, most commonly OVARIAN cancer but includes cancer of cervix, lung, pancreas, bladder, and stomach among others.

-Can occur before, simultaneously, OR after diagnosis of inflammatory myopathy
-All patients with newly diagnosed PM or DM should be evaluated for possible malignancy, including pelvic ultrasound and age-appropriate screening

Treatment

                    First line therapy is GLUCOCORTICOIDS 

–Steroid sparing agents like Azathiprine (check that TPMT level!), Methotrexate, and Hydroxychloroquine (good for skin manifestations) are often added to primary therapy
-IVIG and other therapies used for refractory cases
-Physical therapy
-Aspiration precautions (risk of dysphagia)
-Treatment/Prevention of Osteoporosis as on high dose steroids
-PJP prophylaxis if on high dose steroids (~>20 mg Prednisone/1 month)