Polymyositis and dermatomyositis differential diagnosis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Template:Aditya, Anmol Pitliya, M.B.B.S. M.D.[2]

Overview

Polymyositis and Dermatomyositis must be differentiated from other inflammatory myopathies which cause muscle weakness and systemic symptoms.

Differentiating Polymyositis and Dermatomyositis from other Inflammatory Myopathies

Organ system	Disease	Symptoms												History	Physical Examination	Diagnosis
Organ system	Disease	Age of onset	Muscle weakness	Fever	Myalgia	Contractures	Gait abnormality	Neuropathy	Atrophy	Stiffness	Myoglobinuria	Other features	Laboratory Findings	History	Physical Examination	Creatine Kinase	Muscle Biopsy	Electromyogram
Inflammatory/ Rheumatologic	Dermatomyositis^[1]	40s−50s Can affect children	Proximal	+	+	−	−	−	−	+	−	Rash Dyspnea Weight loss Cough	Viral infections Cancer	Heliotrope rash on face and hands Telangiectasia Erythema Mechanic’s hands Gottron’s sign ( violaceous scaly eruption )	↑↑ ESR ↑↑ CRP	↑↑	Perimysial mononuclear infiltrate	Myopathic
	Polymyositis^[2]	> 18 years	Proximal	+	+	−	−	−	−	+	−	Similar to dermatomyositis without mucous and skin involvement	N/A	N/A	↑↑ ESR ↑↑ CRP	↑↑	Endomysial mononuclear infiltrate Patchy necrosis	Myopathic
	Inclusion body myositis^[3]	50s	Proximal & distal	−	−	−	−	−	−	−	−	Dysphagia Asymmetric weakness	Retrovirus (most common)	N/A	Antibodies to cytoplasmic 5’−nucleotidase	↑↑	Inflammatory cells Invading muscle cells Vacuolar degeneration Inclusions or plaques	Neurogenic
	Fibromyalgia^[4]	40−50s	Generalized	−	−	−	−	+	−	−	−	Anxiety or depression features Fatigue Sleep disturbance Numbness Muscle spasms	History of depression	Tenderness in the soft tissue anatomical location	Normal	Normal	Normal	Normal
	Polymyalgia Rheumatica^[5]	50s	Diffuse	+	+	−	−	−	−	+	−	Weight loss	History of joints stiffness, worse in the morning	Restricted shoulder motion	↑↑ ESR ↑↑ CRP	Normal	Normal	Normal

References

↑ Dalakas MC (1991). “Polymyositis, dermatomyositis and inclusion-body myositis”. N Engl J Med. 325 (21): 1487–98. doi:10.1056/NEJM199111213252107. PMID 1658649.
↑ Dalakas MC (1991). “Polymyositis, dermatomyositis and inclusion-body myositis”. N Engl J Med. 325 (21): 1487–98. doi:10.1056/NEJM199111213252107. PMID 1658649.
↑ Dalakas MC (1991). “Polymyositis, dermatomyositis and inclusion-body myositis”. N Engl J Med. 325 (21): 1487–98. doi:10.1056/NEJM199111213252107. PMID 1658649.
↑ Ohara N, Katada S, Yamada T, Mezaki N, Suzuki H, Suzuki A, Hanyu O, Yoneoka Y, Kawachi I, Shimohata T, Kakita A, Nishizawa M, Sone H (2016). “Fibromyalgia in a Patient with Cushing’s Disease Accompanied by Central Hypothyroidism”. Intern. Med. 55 (21): 3185–3190. doi:10.2169/internalmedicine.55.5926. PMC 5140872. PMID 27803417.
↑ Myklebust G, Gran JT (1996). “A prospective study of 287 patients with polymyalgia rheumatica and temporal arteritis: clinical and laboratory manifestations at onset of disease and at the time of diagnosis”. Br J Rheumatol. 35 (11): 1161–8. PMID 8948307.

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[pmid1658649-1] Dalakas MC (1991). “Polymyositis, dermatomyositis and inclusion-body myositis”. N Engl J Med. 325 (21): 1487–98. doi:10.1056/NEJM199111213252107. PMID 1658649.

[pmid16586492-2] Dalakas MC (1991). “Polymyositis, dermatomyositis and inclusion-body myositis”. N Engl J Med. 325 (21): 1487–98. doi:10.1056/NEJM199111213252107. PMID 1658649.

[pmid16586493-3] Dalakas MC (1991). “Polymyositis, dermatomyositis and inclusion-body myositis”. N Engl J Med. 325 (21): 1487–98. doi:10.1056/NEJM199111213252107. PMID 1658649.

[pmid27803417-4] Ohara N, Katada S, Yamada T, Mezaki N, Suzuki H, Suzuki A, Hanyu O, Yoneoka Y, Kawachi I, Shimohata T, Kakita A, Nishizawa M, Sone H (2016). “Fibromyalgia in a Patient with Cushing’s Disease Accompanied by Central Hypothyroidism”. Intern. Med. 55 (21): 3185–3190. doi:10.2169/internalmedicine.55.5926. PMC 5140872. PMID 27803417.

[pmid8948307-5] Myklebust G, Gran JT (1996). “A prospective study of 287 patients with polymyalgia rheumatica and temporal arteritis: clinical and laboratory manifestations at onset of disease and at the time of diagnosis”. Br J Rheumatol. 35 (11): 1161–8. PMID 8948307.

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