Differentiating dermatomyositis from other diseases

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Dermatomyositis must be differentiated from other common, lymphocyte predominant inflammatory myopathies. Hypothyroidism and sarcoidosis have some symptoms in common with dermatomyositis, and therefore need to be ruled out.

Differentiating Dermatomyositis from other Diseases

Dermatomyositis must be differentiated from other common, lymphocyte predominant inflammatory myopathies. If present, the characteristic perifascicular atrophy makes this distinction trivial.

There is some overlap in the microscopic appearances of different inflammatory myopathies, but some helpful differences are often present. The rimmed vacuoles of inclusion body myositis (IBM) are absent in dermatomyositis. Polymyositis is characterised by diffuse or patchy inflammation of the muscle fascicles, a random pattern of muscle atrophy, and T-cell predominance with T-cells seen invading otherwise viable appearing muscle fibers.

Diseases that can present with similar symptoms as those of dermatomyositis are-

• Hypothyroidism
• Sarcoidosis

Disease	Differentiating signs and symptoms	Diagnostic findings
Fibromyalgia	Symptoms have been present at a similar level for at least 3 months. Chronic musculoskeletal pain with multiple tender points Stiffness, numbness, and fatigue Headaches Sleep disorder	All lab tests are normal
Rheumatoid arthritis	Multiple joint swelling Morning stiffness Rheumatoid nodules	RF or anti-cyclic citrullinated protein (CCP) antibody is positive. Markers of systemic inflammation (ESR, CRP) are typically elevated.
SLE	Maculopapular rash Multi-system involvement	Positive anti-Smith antibodies
Chronic fatigue syndrome	Fatigue plus 4 of the following symptoms: Short-term memory loss Sore throat Tender lymph nodes in the neck or armpit Muscle pain Joint pain without swelling or redness Headaches Insomnia Malaise	Diagnosis of exclusions Symptoms must present for more than 6 months
Spondyloarthritis	Axial skeletal pain and stiffness Restricted spinal motion	Elevated ESR or CRP Negative RF Bamboo spine on x-ray
Polymyalgia rheumatica	Older at onset Generalized stiffness	An elevated erythrocyte sedimentation rate (ESR) OR C-reactive protein (CRP) Response to corticosteroids
Osteoarthritis	Localized joint pain Restricted to affect joints Older at onset	X-ray of the involved joints demonstrate degenerative changes
Hypothyroidism	Systemic symptoms such as weight gain, constipation, dry skin Muscular aching and prominent fatigue that improves on replacement of thyroid hormone.	TSH is elevated and free T4 is low.
Myopathaies (polymyositis and dermatomyositis)	Pelvic and shoulder girdle muscle weakness Rash	Muscle biopsy confirms the diagnosis Elevated CPK enzyme
Neuropathy	Numbness and tingling Paresthesia	Abnormal EMG