What are the differential diagnoses for fibromyalgia?

Differential Diagnosis of Fibromyalgia

The differential diagnosis for fibromyalgia must exclude inflammatory, endocrine, and structural conditions that can mimic widespread pain, while recognizing that fibromyalgia is a positive clinical diagnosis based on central sensitization—not a diagnosis of exclusion. 1, 2

Rheumatologic and Inflammatory Conditions

• Rheumatoid arthritis should be excluded through clinical examination for synovitis, joint swelling, and elevated inflammatory markers (ESR, CRP), as fibromyalgia characteristically has normal inflammatory markers 1
• Systemic lupus erythematosus can present with widespread pain and fatigue but typically shows positive ANA, specific autoantibodies, and organ involvement not seen in fibromyalgia 3
• Polymyalgia rheumatica presents with proximal muscle pain and stiffness but shows markedly elevated ESR/CRP and responds dramatically to low-dose corticosteroids 3
• Polymyositis/dermatomyositis causes muscle weakness (not just pain) with elevated creatine kinase levels, which should be checked as part of basic screening 1

Endocrine and Metabolic Disorders

• Hypothyroidism mimics fibromyalgia with fatigue, myalgias, and cognitive dysfunction but is identified through thyroid function testing (TSH, free T4) 1
• Vitamin D deficiency causes diffuse musculoskeletal pain and should be measured, as it is easily correctable 1
• Hyperparathyroidism can present with bone pain, fatigue, and cognitive symptoms but shows elevated calcium and parathyroid hormone levels 3

Neurologic Conditions

• Cervical radiculopathy from disc herniation or foraminal stenosis causes pain in dermatomal distributions with associated neck pain, requiring cervical spine MRI if suspected 4
• Peripheral neuropathy from diabetes, B12 deficiency, or other metabolic causes typically presents with distal, symmetric sensory symptoms rather than widespread pain 4
• Multiple sclerosis may present with fatigue and pain but shows focal neurologic deficits and characteristic MRI findings 3

Functional Somatic Syndromes (Overlapping Conditions)

• Chronic fatigue syndrome may coexist with or present similarly to fibromyalgia, sharing features of profound fatigue, sleep disturbance, and cognitive dysfunction 1, 3
• Irritable bowel syndrome frequently coexists with fibromyalgia as both are central sensitization disorders 3, 5
• Migraine headaches commonly overlap with fibromyalgia and may represent the same underlying central pain processing abnormality 1, 5
• Temporomandibular disorder and other regional pain syndromes may coaggregate with fibromyalgia 5

Infectious and Post-Infectious Conditions

• Post-Lyme disease syndrome can present with multiple tender points and widespread pain that fulfills fibromyalgia criteria, requiring careful history of tick exposure and Lyme serology 1
• Chronic viral infections (hepatitis C, HIV) can cause fatigue and myalgias but are identified through specific serologic testing 3

Psychiatric Conditions

• Major depressive disorder shares symptoms of fatigue, sleep disturbance, and cognitive dysfunction but is distinguished by primary mood disturbance, anhedonia, and hopelessness 3
• Generalized anxiety disorder may present with muscle tension and fatigue but lacks the characteristic widespread hyperalgesia of fibromyalgia 6
• Somatization disorder involves multiple physical complaints across organ systems but lacks the specific pattern of central pain amplification 3

Myopathies and Muscle Disorders

• Statin-induced myopathy causes muscle pain and weakness with elevated creatine kinase, requiring medication history review 1
• Myofascial pain syndrome involves localized trigger points rather than the diffuse tender points and widespread pain of fibromyalgia 3

Critical Diagnostic Approach

• Basic laboratory screening must include ESR, CRP, thyroid function tests, creatine kinase, vitamin D, complete blood count, and comprehensive metabolic panel to exclude mimicking conditions 1
• Avoid the pitfall of treating fibromyalgia as a diagnosis of exclusion; instead, make a positive diagnosis based on characteristic features of central sensitization with chronic widespread pain lasting at least 3 months, accompanied by fatigue, sleep disturbances, and cognitive dysfunction 1, 2
• Normal laboratory results and imaging support rather than exclude the diagnosis of fibromyalgia, as it is fundamentally a central nervous system disorder without peripheral tissue damage 2