Dermatomyositis
For a diagnosis of dermatomyositis, patients must present with at least one of the following skin symptoms:
- Heliotrope rash – a red/purple rash with swelling on the upper eyelid
- Periungual telangiectasias – dilated capillaries at the skin folds around the fingernails, appearing as small red dots
- Gottron’s sign or papules – red/purple hardened or eroding areas of skin on the upper surface of finger joints or over the elbows or knees
- Shawl sign, V-sign, and holster sign – characteristic red, sometimes raised rashes distributed in a “shawl” pattern over the shoulders, arms, and upper back, in a V-shaped pattern over the front of the neck and chest, and over the outside of the hip
- Skin biopsy demonstrating reduced capillary density, deposits of membrane attack complex on small blood vessels along the dermal-epidermal junction, and within the walls of dermal blood vessels
A diagnosis of dermatomyositis must also have at least four of the following criteria:
- Symmetrical muscle weakness in the shoulders/upper arms or hips/upper legs and trunk
- Elevation of serum levels of skeletal muscle-associated enzymes: CK, aldolase, lactate dehydrogenase (LD or LDH), transaminases (ALT/SGPT and AST/SGOT)
- Muscle pain on grasping or spontaneous pain
- The triad of muscle-related changes on EMG:
- Short, small, low-amplitude polyphasic motor unit potentials
- Fibrillation potentials, even at rest
- Bizarre high-frequency repetitive discharges
- Positive for any of the myositis-specific autoantibodies
- Nondestructive arthritis or arthralgias
- Signs of systemic inflammation
- Fever
- Elevated serum C-reactive protein (CRP) level, or
- Accelerated erythrocyte sedimentation rate (ESR)
- Muscle biopsy findings compatible with inflammatory myositis:
- Perivascular inflammation with predominantly B-cells (with smaller numbers of CD4-positive T-cells) accumulated around blood vessels
- Perifascicular atrophy
- Vasculitis involving endomysial and perimysial capillaries and arterioles
- Active phagocytosis
- Central nuclei, or
- Active regeneration
Amyopathic dermatomyositis (that is, dermatomyositis without symptoms of muscle pain and weakness) has some unique diagnostic considerations.