Polymyositis/Dermatomyositis Flashcards
What is polymyositis?
A type of chronic inflammation of the muscles (inflammatory myopathy) related to dermatomyositis and inclusion body myositis. Its name means “inflammation of many muscles” (poly- + myos- + -itis).
Polymyositis is an inflammatory myopathy mediated by cytotoxic T cells with an as yet unknown autoantigen, while dermatomyositis is a humorally mediated angiopathy resulting in myositis and a typical dermatitis.
What are features of polymyositis?
- Progressive symmetrical muscle weakness - proximal musculature of the upper and lower limbs
- Myalgia +/- arthralgia
- Weight loss
- Fatigue/tiredness
Besides proximal limb weakness, what other forms of muscle weakness can occur in polymyositis?
- Oesophageal - Dysphagia
- Respiratory muscles - Dyspnoea
- Laryngeal muscles - Dysphonia
What can myositis be caused by?
- Idiopathic
- Paraneoplastic syndrome
What type of myositis is most commonly associated with malignancy?
Dermatomyositis
What is cancer associated myositis?
Myositis caused by paraneoplastic syndrome
What are the features of dermatomyositis?
Myositis, plus skin signs
-
Macular rash
- Shawl Sign - if back and shoulders
- Lilac-purple (heliotrope) rash + oedema - eyelids
- Nailfold erythema
- Gattron’s papules
- V-Sign
- Subcut calcification
What are Gottron’s papules?
Violaceous (violet-coloured) papular rash on the dorsal aspect of the interphalangeal joints
What is the following?
Dermatomyositis
Usually described as a macular, confluent, purple or violaceous rash over both eyelids and periorbital tissue. It can present with or without oedema.
What is the following?
V-Sign
A confluent, macular, violet/red rash seen over the anterior neck and upper chest. Often found in a V-shape similar to the neck of a shirt.
What is the following?
Shawl’s Sign
A confluent, violaceous, macular rash over the posterior shoulders and neck.
What is proximal myopathy?
A muscle disorder which results in proximal muscle group weakness e.g:
- Shoulder: pectoralis major, deltoid, biceps
- Hip: gluteal, quadriceps, iliopsoas, adductor
Why does proximal muscle weakness occur in dermatomyositis?
Complement and antibody destruction of microvasculature; the deposition of complement and antibody complexes leads to inflammation and destruction of muscle fibres and hence weakness
What causes muscle weakness in polymyositis?
T-cell (in particular CD8) and macrophage destruction of muscle fibres
What are extramuscular signs of Polymyositis/Dermatomyositis?
- Fever
- Arthralgia
- Raynaud’s
- Interstitial lung fibrosis
- Myocarditis
- Arrhythmias
How would you investigate someone with suspected polymyositis/dermatomyositis?
Bloods
- Serum Muscle enzymes
- ESR + CRP
- Autoantibodies
Scans
- PET
- MRI
Other
- EMG
- Biopsy
What is the following?
Calcinosis - calcium deposits under the skin
What serum muscle enzymes would you look at when investigating suspected myositis?
- CK
- Aldolase
- ALT
- AST
- LDH
Why might you do a PET scan in someone presenting with myositis?
Look for underlying malignancy
What auto-antibodies would you look for in myositis?
- Anti-Mi2
- Anti-Jo1
- ANA - associated wtih DM
What is the presence of anti-Jo1 and anti-Mi2 associated with in myositis related conditions?
Acute onset and interstitial lung fibrosis
If someone presented with symptoms of myositis, what would be your differential?
- Carcinomatous myopathy
- Inclusion body myositis
- Muscular dystrophy
- PMR
- Endocrine/metabolic myopathy
- Rhabdomyolysis
- Infection
- Drugs
How would you manage dermato/polymyositis?
- Prednisolone
- Immunosuppression if resistant
- Topical tacrolimus/ hydroxychloroquine for skin disease
SCREEN FOR MALIGNANCY
What are complications of dermatomyositis?
- Aspiration pneumonia
- Interstitial pulmonary fibrosis
- Cardiomyopathy
- Muscle atrophy
- Muscle calcification
What antibodies are associated with dermatomyositis?
- Anti-Mi2
- Anti-Jo1
What antibodies are implicated in both dermatomyositis and polymyositis?
Anti-synthase antibodies
What diseases can dermatomyositis be associated with, and what investigations would you consider doing to look for a cause?
Cancers:
- Imaging e.g. CXR, MRI/CT, Endoscopy etc.
