Inflammatory myopathies (dermatomyositis, polymyositis) Flashcards
Describe this skin lesion over the face
Heliotrope rash around the eyes
- Purple/violet colour symmetrical distribution over periorbital skin with subcutaneous oedema
(derived from heliotropium - purple flower)
Describe this skin lesion over the hands
What are the causes that may resemble such changes?
Gottron papules - flat topped, violaceous, scaly papules or plaques over knuckles, elbows and knees
- Can have thick psoriasiform scale
- Most prominent over bony prominences, esp MCP, PIP and DIP, elbows, knees, feet
Other causes resembling such lesions:
1. SLE
2. Psoriasis
3. Lichen planus
4. Drug-induced changes - hydroxyurea, penicillamine, statin, quinidine, phenylbutazone
Describe this skin lesion
Shawl sign - hyperpigmentation and telangiectasia (termed poikiloderma) over sun-exposed skin
- Photosensitive distribution
- Mainly V shaped over neck and upper chest
- Other sites: extensors of arm, back
Clinical findings of dermatomyositis
- Pathognomic cutaneous feature + muscle weakness
A. Cutaneous manifestations
1. Heliotrope rash
2. Gottron papules and palm hyperkeratosis
3. Subcutaneous oedema
4. Violaceous rash on extensors
5. Photosensitive rashes and hyperpigmentation
6. Telangiectasia
- Periungal (nail telangiectasia)
- Poikiloderma (sun exposed skin telangiectasia) - shawl sign
7. Raynaud’s syndrome
8. Non-scarring alopecia
9. Ichthyosis
10. Buccal mucosa white plaques
11. Cutaneous vasculitis
12. Calcinosis
12. Ulcerative skin lesions - highly associated with malignancy
B. Proximal muscle weakness and tenderness
C. Other manifestations
1. Malignancy - lung, GI, breast, ovarian, prostate
2. Arthritis
3. Dysphagia
4. Interstitial lung disease
Classification of idiopathic inflammatory myopathies
- Adult onset dermatomyositis
- Myotrophic dermatomyositis
- Amyotrophic dermatomyositis - Overlap myositis
- Anti-synthetase antibody syndrome
- CTD related myositis - Adult onset polymyositis
- Immune mediated necrotising myositis
- Inclusion body myositis
- Juvenile onset dermatomyositis
Dermatomyositis is an idiopathic inflammatory myopathy with characteristic:
1. Proximal muscle weakness and pain
2. Cutaneous features
3. Joint, oesophagus, lung involvement
It can occur as Idiopathic autoimmune, drug-induced or possible malignancy in patients > 40 years old.
Some patients may have dermatomyositis-sine myositis (also known as amyotrophic DM) - cutaneous manifestation without muscle weakness (muscle enzyme level remained normal for at least 2 years)
Epidemiology of dermatomyositis
Bimodal age peak: 5-15 years and 45-65 years
Female > male (3:1)
African-Americans predominance
Drug-induced dermatomyositis
- Hydroxyurea
- Penicillamine
- Statin
- Quinidine
- Phenylbutazone
Diagnostic criteria for dermatomyositis
Clinical criteria
1. Proximal motor weakness
1A. Striated muscle groups: pharyngeal, upper oesophageal muscle (dysphagia, nasal regurgitation, aspiration pneumonia)
2. Characteristic skin rashes
Laboratory criteria
2. Elevated CK or aldolase
3. Myositis associated autoantibodies
4. Abnormal EMG
5. Muscle biopsy
Clinical features of polymyositis
- Proximal muscle weakness WITHOUT skin changes
- Elevated muscle enzyme not due to other causes
- 30% cardiac involvement (conduction defect, heart failure)
- Risk of malignancy
Association between PM/DM and underlying neoplastic disease
Termed: cancer associated myositis
10% to 20% of middle aged adult
>50% over age 65 years
80% have dermatomyositis, 20% have polymyositis
Common cancers: lung adenoca, breast, lung, pancreas, stomach, colon, ovary, Hodgkin’s lymphoma, leukaemia
Asians: NPC, cervical tumours
Investigations for dermatomyositis/polymyositis
Defining investigations
1. Serum creatine kinase (CK), aldolase
2. Myositis associated autoantibodies (see subsequent card)
3. Electromyography (EMG)
4. Muscle biopsy
Other important investigations
5. LFT - Elevated AST
6. ANA
7. MRI of muscle
8. CT TAP - TRO malignancy
9. Tumour markers - CEA, CA125, CA19.9, CA15.3
Myositis associated antibodies
DM/PM
1. Anti-Mi2
2. Anti-MDA5 (melanoma differentiation)
3. Anti-TiF-1-gamma (highly associated with malignancy)
4. Anti-NXP2 or MJ (nuclear matrix protein 2)
5. Anti-SAE (small ubiquitin-like activating enzyme)
ASA
1. Anti-Jo-1
2. Anti-PL-7 and PL-12
3. Anti-EJ
4. Anti-OJ
EMG findings in dermatomyositis/polymyositis
- Increased insertional activity with spontaneous fibrillation
- Low amplitude, short duration
- Complex repetitive discharges
Clinical considerations of muscle biopsy
- Biopsy muscle that is clearly weak but not severely
- Biopsy muscle contralateral to abnormal EMG
- Do not biopsy EMG-ed muscle (spurious result)
- Do not biopsy rhabdomyolysis muscle within 3 months of episode
Muscle biopsy findings of dermatomyositis/polymyositis
- Perimysial/perivascular inflammation with/without perifascicular atrophy
- B cell, CD+ T cell, dendritic cells infiltrate
Management of dermatomyositis/polymyositis
Non-pharmacological
1. MDT - PT, OT, rheumatology, patient education
2. PT prevents contractures
3. Bed rest for severe inflammation
4. Avoid sunlight, use sunscreen
5. Identifying potential malignancy
Pharmacological
6. High dose steroid therapy
7. Hydroxychloroquine, azathioprine, methotrexate, MMF as steroid sparing agent
8. Consider tacrolimus or rituximab
9. High dose IVIG for 6 months (refractory)
