Muscles may be painful and tender in 60% of cases though onset is often painless.
Proximal muscles are first involved and initially weakness may be asymmetrical, e.g. one quadriceps only.
Weakness of posterior neck muscles will result in the head 'lolling' forwards.
Occasionally weakness may spread into distal limb muscle groups.
Pharyngeal and laryngeal involvement results in dysphagia and dysphonia. Cardiac muscle may also be involved. Respiratory muscle weakness causes respiratory failure (this may be disproportionately severe).
The eye muscles are not involved unless there is coexistent myasthenia gravis.
Reflexes are retained (if absent, consider underlying carcinoma with added neuropathy).
Often more severe and acute Characterised by skin rash. Violet discoloration of light exposed skin. /•«•»Hy
- Heliotropic discolouration of eyelids Raised scaly erythematosus rash involving nose and cheeks, shoulders, extensor surfaces of limbs and knuckles
Telangiectasia and tightening of skin are common and small ulcerated vasculitic lesions develop over bony prominences.
Multisystem involvement. Calcification develops in skin and muscle with extrusion through skin.
Muscle contractures develop - tip-toe gait.
Gastrointestinal ulceration occurs.
The muscle weakness is as in polymyositis but in childhood dermatomyositis may be very severe, involving chewing, swallowing and breathing.
Inclusion body myositis.
Acid Maltase deficiency (presenting as respiratory failure)
Limb girdle dystrophy.
Drug induced, toxic and metabolic myopathies.
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