Myositis - polymyositis + dermatomyositis Flashcards
What is myositis?
CTDs characterised by inflammation of muscles
Includes polymyositis and dermatomyositis (most common types)
Other types = necrotising autoimmune myopathy and sporadic inclusion body myositis (IBM)
TRUE OR FALSE
Dermatomyositis mainly affects the skin
FALSE
It can affect other body parts e.g., joints, oesophagus, lungs and heart
Which viral infections have been implicated in poly- + dermatomyositis?
HIV
Human T-cell lymphotropic virus type I (HTLV-I)
Simian retroviruses
Cocksackievirus B
What is the incidence of dermatomyositis?
1.4 cases per 100,000
What is the prevalence of dermatomyositis?
5.8 cases per 100,000
Higher prevalence amongst older age group
TRUE OR FALSE
Women are more likely to be affected by dermatomyositis than men
TRUE
What is the incidence of polymyositis?
3.8 cases per 100,000
What is the prevalence of polymyositis?
9.7 cases per 100,000
Is the onset of polymyositis slow or fast?
Gradual
Onset over weeks or months
Steady progression
In which muscle groups does muscle weakness develop?
Proximal muscles
Which actions does proximal myopathy make more difficult?
Rising from a chair
Climbing stairs
Lifting objects
Combing hair
Apart from diffuse weakness, what other symptoms may be present in polymyositis?
Fatigue
Myalgia
Muscle cramps
Dysphagia - caused by pharyngeal weakness
Which muscle groups are spared in polymyositis? Hence what are patients still able to do?
Distal muscles spared
Patients can still do fine motor movements of hand e.g., :
- buttoning a shirt
- writing
- operating a keyboard
- playing the piano
Affected only late in the disease
Is the weakness in polymyositis always at a constant level?
No
May vary from week to week or month to month
What proportion of patients with polymyositis have pain?
1/3
Hence not usually painful in most patients
Is there a skin rash in polymyositis?
No
What would there be no FHx of in polymyositis?
Neuromuscular disease
Also no evidence of endocrine disorder or Hx of exposure to possible toxins
What may you see on examination of a patient with polymyositis?
Proximal muscle weakness, sparing of distal muscles until disease is well advanced
External ocular muscles unaffected
Facial muscles affected only in severe disease
Weak forced flexion of neck - there could be difficulty holding the neck up
Muscular atrophy with preservation of tendon reflexes, flexor plantar response and normal sensation
Muscles may be tender on palpation with a nodular grainy feel
What investigations would you do for polymyositis and what would you expect to find?
Creatine kinase - up to 50 times normal (rarely normal in active disease - good indication of disease activity)
Anti-Jo-1 antibodies - in 20%
Other enzymes = aldolase, serum glutamic-oxaloacetic transaminase (SOGT), serum glutamic-pyruvic transaminase (SGPT) and LDH
EMG + confirmed by muscle biopsy - definitive test for polymyositis
CA 125, CA 19-9 - useful markers for malignancy
Myositis-specific antibody (MSA) and myositis-associated autoantibodies (MMA) - useful for differentiating patients with underlying malignancy
If a patient with polymyositis have anti-Jo-1 antibodies, is this a good or bad prognosis?
Poor prognosis, with interstitial lung disease which occurs in about 1/3
In polymyositis if SGOT is higher than SGPT what type of cause should be suspected?
Myogenic cause
What are the other DDx for polymyositis?
Hereditary neuromuscular diseases
Endocrine disease inc. thyrotoxicosis and Cushing’s disease
Malabsorption syndromes e.g., alcoholism, cancer, vasculitis, granulomatous disease, sarcoidosis or exposure to drugs or toxins that affect the muscles
TRUE OR FALSE
Dermatomyositis affects both children and adults
TRUE
What pattern of muscle weakness does dermatomyositis have?
Same as polymyositis
