What are the common differential diagnoses for fatigue?

Common Differential Diagnoses for Fatigue

The most common causes of fatigue in primary care are depression (18.5%), followed by serious somatic disease (4.3%), anemia (2.8%), and malignancy (0.6%), with psychiatric disorders being far more prevalent than organic disease. 1

Systematic Approach to Differential Diagnosis

Psychiatric and Psychosocial Causes (Most Common)

• Depression is the leading identifiable cause of fatigue, occurring in approximately 18.5% of patients presenting with tiredness. 1
• Screen all patients with the two-question depression screen: "In the last month, have you often felt dejected, sad, depressed or hopeless?" and "In the last month, did you experience significantly less pleasure than usual with the things you normally like to do?" 2
• Anxiety disorders, somatoform disorders, and chronic stress are also frequent contributors to fatigue. 3
• Psychosocial stress and lifestyle derangements are common underlying factors. 1

Endocrine and Metabolic Disorders

• Hypothyroidism presents with fatigue, weight changes, hair loss, cold intolerance, constipation, and depression. 4
• Adrenal insufficiency manifests with fatigue, mood changes, and can be associated with other endocrine abnormalities. 4
• Diabetes mellitus causes fatigue, mood changes, and polyuria. 4
• Hypogonadism and hypopituitarism should be considered, especially in patients with multiple hormone deficiencies. 5
• Vitamin D deficiency, low IGF-1, and magnesium deficiency correlate with muscle fatigue. 5

Hematologic Causes

• Anemia occurs in approximately 2.8% of patients presenting with fatigue and is a highly treatable cause. 1
• Complete blood count with differential is mandatory for all patients with moderate-to-severe fatigue (score ≥4). 5

Inflammatory and Autoimmune Conditions

• Polymyalgia rheumatica-like syndrome presents with severe proximal myalgia in upper/lower extremities with fatigue, highly elevated inflammatory markers, but normal creatine kinase levels. 5
• Inflammatory arthritis can present as oligoarthritis of large joints or symmetrical polyarthritis resembling rheumatoid arthritis, with possible positive rheumatoid factor or anti-CCP antibodies. 5
• Systemic lupus erythematosus should be considered in the appropriate clinical context. 2

Sleep Disorders

• Obstructive sleep apnea, restless leg syndrome, and periodic limb movement disorder require evaluation through detailed sleep history. 2
• Insomnia and other sleep disturbances are common comorbid conditions. 4

Medication-Related Causes

• Review all current medications and supplements for fatigue-inducing side effects. 5
• Statin-induced myopathy presents with myalgia and normal-to-mildly elevated creatine kinase. 5

Malignancy and Serious Organic Disease

• Malignancy is rare, occurring in only 0.6% of patients presenting with fatigue. 1
• Serious somatic disease occurs in approximately 4.3% of cases. 1
• Importantly, the prevalence of somatic disease is identical in patients with and without tiredness, suggesting the association may not be causal. 1

Chronic Fatigue Syndrome (ME/CFS)

• Diagnosis requires exclusion of other medical and psychiatric conditions that could explain the fatigue. 2
• Characterized by persistent, debilitating fatigue not alleviated by rest and often worsening with physical or mental exertion. 6
• Associated symptoms include cognitive impairments, post-exertional malaise, muscle and joint pain, sleep disturbances, and immune system dysfunction. 6

Mandatory Laboratory Evaluation

For patients with moderate-to-severe fatigue (score ≥4 on 0-10 scale), perform the following initial workup: 5, 4

• Complete blood count with differential 5
• Comprehensive metabolic panel 5
• Thyroid function tests (TSH, free T4) 4
• Morning cortisol and ACTH (ideally around 8 AM) 4
• Inflammatory markers (CRP, ESR) 5
• Creatine kinase 5
• Fasting glucose or HbA1c 4
• Vitamin D level 4
• Urinalysis 2

Critical caveat: Laboratory results affect management in only approximately 5% of cases, but are essential to exclude treatable causes. 2, 7

Key Clinical Pitfalls

• Extensive investigations are only warranted with specific findings from history or clinical examination, as serious somatic disease is rare. 1
• If initial laboratory results are normal, repeat testing is generally not indicated. 7
• If adrenal insufficiency and hypothyroidism coexist, steroids must always be started before thyroid hormone replacement to avoid precipitating an adrenal crisis. 4
• Patients often believe they are suffering from an organic medical disorder and resist psychiatric labeling of their symptoms. 3
• Attention should focus on depression and psychosocial problems rather than extensive organic workup in the absence of specific clinical findings. 1