Polymyositis and Dermatomyositis

Question 1

Define:

Answer 1

• Connective tissue diseases characterised by inflammation of muscles.
• Characterised by insidious onset of progressive symmetrical proximal muscle weakness and autoimmune mediated striated muscle inflammation (myositis) associated with myalgia +/- arthralgia

Question 2

Aetiology/risk factors:

Answer 2

UNKNOWN
Has an association with viral infections
Dermato has myositis as well as skin changes

Question 3

Epidemiology:

Answer 3

• RARE
• Polymyositis presents between 30-60 yrs
• Dermatomyositis can occur at any age (peak onset: 5-10 (children) and 50 (adults))
• Both diseases are 2 x more common in FEMALES

Question 4

Symptoms of polymyositis:

Answer 4

o Inflammatory myopathy with onset over weeks or months
o Steady progression of symptoms
o Diffuse weakness in proximal muscles
• Causing difficulty rising from a low chair, climbing steps, lifting objects and combing hair
• Also fatigue, myalgia and muscle cramps
o Distal muscles are spared - so fine motor coordination tends to be preserved in the early stages
o Pharyngeal weakness –> dysphagia
o Dysphonia
o Respiratory weakness
o NO rash

Question 5

Symptoms of dermatomyositis:

Answer 5

o Inflammatory myopathy with onset over weeks or months
o RASH
o Systemic upset with fever, arthralgia, malaise and weight loss
o Possible cardiac disease (e.g. conduction blocks, tachyarrhythmia)
o GI ulcers and infections
o Interstitial lung disease (30-50%)
o Children have more non-muscular features (e.g. GI ulcers and infections)

Question 6

Signs of polymyositis:

Answer 6

o	Fever		
o	Muscle weakness 
o	NOT painful in most patients
o	Proximal myopathy 
o	Extraocular muscles and distal muscles are spared
o	Weak forced flexion of the neck 
o	Muscular atrophy 
o	Muscles may be tender on palpation

Question 7

Signs of dermatomyositis:

Answer 7

o RASH characteristics
• Macular rash: shawl sign = rash over back and shoulders
• Lilac-purple heliotrope rash on eyelids often with oedema
• Nailfold erythema
• Gottron’s papules: roughened red papules over knuckles, elbows and knees
o Rash may affect knees, shoulders, back and upper arms
o Rash may be exacerbated by sunlight
o Proximal myopathy
o Muscle pain and tenderness in early disease
o Fever

Question 8

Investigations of polymyositis:

Answer 8

o Creatine kinase - up to 50 x higher than normal
o Electromyography (EMG)
o Muscle biopsy - DEFINITIVE TEST
o Autoantibodies (e.g. myositis specific antibody, anti-Jo-1 antibody)
o Enzymes (e.g. SGOT, SGPT, LDH, ALT, AST, aldolase)

Question 9

Investigations of dermatomyositis:

Answer 9

o Creatine kinase - not as reliable as in polymyositis
o Enzymes (SGOT, SGPT and LDH, ALT, AST, aldolase may be raised)
o Autoantibodies
• ANA
• Anti-Mi-2
• Anti-Jo-1 (more common in polymyositis)
o EMG - may be helpful but can be normal as well
o Muscle biopsy