Dermatomyositis and Polymyositis

Question 1

What is dermatomyositis and polymyositis associated with?

Answer 1

Malignancy (30-40% of patients)

• DM/PM may be part of paraneoplastic syndromes esp 2’ lung, pancreatic, ovarian or bowel malignancy
• DM/PM may precede malignancy by 2-3 years -> search for occult malig in recurrent, refractory or ANA –ve DM
• Most common malignancies are Gastric and NPC (hence OGD and Nasopharyngoscope)

Overlap syndrome w other CTDs (eg SLE, scleroderma)

HLA B8/DR3

Question 2

What is the presentation of dermatomyositis and polymyositis?

Answer 2

Muscle weakness (DM and PM)

• Subacute/insidious onset of symmetrical proximal muscle weakness - difficulty climbing stairs, getting up from a chair, lifting up arms (when bathing yourself etc)
• May have mild myalgia +- arthralgia
• Acute phase: a/w constitutional symptoms
• Chronic phase (if untreated): a/w involvement of pharyngeal, laryngeal and respi muscles -> dysphagia, dysphonia and respiratory failure

Cutaneous features (DM)
- Characteristic rash, often precedes/accompanies weakness 

Periungal erythema and telangiectasia

Ulcerative vasculitis and subcutaneous calcinosis (25%)
- In the long term, muscle fibrosis and contractures of joints may occur

Question 3

What are the skin symptoms & signs of dermatomyositis and polymyositis?

Answer 3

CRUST

• Calcinosis,
• Raynaud phenomenon,
• Ulceration of fingertips (mechanic’s hands),
• Signs specific to DM,
• Telangiectasia (periungal)

Signs specific to DM:

• Gottron’s papules (*Pathognomonic if ↑CK + muscle weakness): flat-topped violaceous papules over extensor surface of MCPJ and IPJ, also elbows and knees
• Heliotrope rash: lilac purple eruptions over upper eyelid, often a/w peri-orbital erythema
• Holster sign: erythema over hip
• Shawl sign: rash across upper back and shoulders
• V sign: rash between breast

Question 4

What are the cardiac features of dermatomyositis and polymyositis?

Answer 4

• Arrhythmias

- Cardiomyopathy

Question 5

What are the respi features of dermatomyositis and polymyositis?

Answer 5

• Respiratory muscle weakness

- ILD -> confirm w HRCT and pulmonary fx test

Question 6

What are the GI features of dermatomyositis and polymyositis?

Answer 6

• Esophageal dysmotility and dysphagia

Question 7

What are the renal features of dermatomyositis and polymyositis?

Answer 7

Nephrotic syndrome

Question 8

What are the skeletomuscular features of dermatomyositis and polymyositis?

Answer 8

• Polyarthritis

- Muscle weakness described in diagnostic criteria

Question 9

What are the investigations to be performed for dermatomyositis and polymyositis?

Answer 9

Raised muscle enzymes: ↑ CK, ALT AST LDH aldolase

EMG: characteristic triad of changes

• Increased insertional activity, fibrillation, & sharp +ve waves
• Spontaneous, bizarre, high frequency discharges
• Polyphasic motor-unit potentials of low amplitude and short duration

Muscle biopsy

MRI: muscle edema in acute myositis

Skin: characteristic lesions +/- skin biopsy (to confirm dx)

Serum auto-ab: ANA, RF, Anti-Mi2 anti-Jo (myositis spef ab)

Evaluation for systemic complications

• Anti-Jo1: 50-75% develop ILD
• ECG, CXR
• Barium swallow: if oesophageal dysmotility suspected

Evaluation for malignancy

• Consider age-appropriate cancer screening
• Bloods: FBC, RP, LFT, tumour markers
• Urine: UFEME
• Radiographic: CXR, CTAP, mammogram, pelvic U/S
• Endoscopic: OGD, colonoscopy, flexible nasendoscopy (?NPC)
• Others: pap smear, DRE

Question 10

What is the management of polymyositis and dermatomyositis?

Answer 10

Adult PM/DM
• Bed rest, combined w exercise programme
- Treatment: PO Pred 0.5-1.0mg/kg, continue for ≥1 mth after myositis has become clinically and enzymatically inactive
- Resistance/relapse: Immunosuppressants, KIV IVIG in recalcitrant cases

Childhood DM
- More intensive, w earlier use of immunosuppressants