Introduction
Dermatomyositis an inflammatory disorder causing symmetrical, proximal muscle weakness and characteristic skin lesions.
Epidemiology
- Incidence: 1.00 cases per 100,000 person-years
- Peak incidence: 50-60 years
- Sex ratio: more common in females 2:1
| <1 | 1-5 | 6+ | 16+ | 30+ | 40+ | 50+ | 60+ | 70+ | 80+ |
Pathophysiology
Pathophysiology
- may be idiopathic or associated with connective tissue disorders or underlying malignancy (typically ovarian, breast and lung cancer, found in 20-25% - more if patient older). Screening for an underlying malignancy is usually performed following a diagnosis of dermatomyositis
- polymyositis is a variant of the disease where skin manifestations are not prominent
Clinical features
Skin features
Other features
- photosensitive
- macular rash over back and shoulder
- heliotrope rash in the periorbital region
- Gottron's papules - roughened red papules over extensor surfaces of fingers
- 'mechanic's hands': extremely dry and scaly hands with linear 'cracks' on the palmar and lateral aspects of the fingers
- nail fold capillary dilatation
Other features
- proximal muscle weakness +/- tenderness
- Raynaud's
- respiratory muscle weakness
- interstitial lung disease: e.g. Fibrosing alveolitis or organising pneumonia
- dysphagia, dysphonia
Investigations
Antibodies
Creatine kinase is elevated.
Skin and muscle biopsies may be done to confirm the diagnosis.
Electromyography
- the majority of patients (around 80%) are ANA positive
- around 30% of patients have antibodies to aminoacyl-tRNA synthetases (anti-synthetase antibodies), including:
- antibodies against histidine-tRNA ligase (also called Jo-1)
- antibodies to signal recognition particle (SRP)
- anti-Mi-2 antibodies
Creatine kinase is elevated.
Skin and muscle biopsies may be done to confirm the diagnosis.
Electromyography
- useful in distinguishing myopathy from neuropathy
Management
Management
- prednisolone