What are the causes of fatigue?

Causes of Fatigue

Fatigue is commonly caused by pain, emotional distress, sleep disturbance, anemia, poor nutrition, decreased activity level, medication side effects, alcohol/substance abuse, and comorbidities. 1

Common Causative Factors

Physical Factors

• Pain - Often clusters with fatigue and requires assessment and effective treatment 1
• Anemia - Should be evaluated through complete blood count and iron studies 1, 2
• Sleep disorders - Range from hypersomnia to insomnia, affecting 30-75% of patients with fatigue 1
• Poor sleep hygiene - Contributing factors include irregular sleep schedules, daytime napping, and caffeine/alcohol consumption before bed 1
• Nutritional deficiencies - Weight changes, caloric intake alterations, and electrolyte imbalances can contribute to fatigue 1
• Decreased physical activity - Deconditioning can worsen fatigue symptoms 1
• Medication side effects - Many medications can cause sedation and fatigue as side effects 1, 3

Psychological Factors

• Depression - Frequently co-occurs with fatigue; studies show 25-33% of patients with fatigue also experience depression 1
• Anxiety - Often accompanies fatigue and requires specific assessment 1
• Emotional distress - Can both cause and exacerbate fatigue symptoms 1

Medical Conditions

• Cancer and cancer treatments - Cause fatigue in 70-90% of patients 4
• Endocrine disorders - Thyroid dysfunction, adrenal disorders, and gonadal dysfunction commonly present with fatigue 5
• Metabolic abnormalities - Hyper/hypoglycemia and dyslipidemia can contribute to fatigue 5
• Sleep apnea - Can develop from changes in body composition or hormone status 1, 6
• Comorbid medical conditions - Various chronic diseases can cause persistent fatigue 1, 7

Evaluation Approach

Initial Assessment

• Use a numeric rating scale (0-10) to quantify fatigue severity 3
• Conduct a thorough review of systems to identify affected organ systems 1, 3
• Evaluate onset, pattern, duration, and changes in fatigue over time 1, 3

Laboratory Workup

• Core tests for moderate to severe fatigue should include:
  • Complete blood count to assess for anemia 2
  • Thyroid-stimulating hormone to screen for thyroid dysfunction 2
  • Basic metabolic panel to evaluate electrolyte imbalances 2
  • Liver function tests 2
  • Inflammatory markers like C-reactive protein 2

Special Considerations

• Fatigue rarely occurs in isolation and often clusters with other symptoms 1, 8
• Laboratory results affect management in only about 5% of fatigue cases but are essential to rule out treatable causes 2, 9
• Cancer is a rare cause of fatigue (0.6% of cases) when fatigue is the only symptom 7

Common Pitfalls in Fatigue Evaluation

• Overlooking psychological causes - Depression and anxiety are frequently missed contributors to fatigue 1
• Focusing exclusively on rare causes - Common causes like sleep disorders and stress account for most cases 7
• Excessive testing - If initial results are normal, repeat testing is generally not indicated 9
• Ignoring medication side effects - Many medications can cause or worsen fatigue 1, 3
• Missing sleep disorders - Sleep disturbances are prevalent but often neglected 1

Remember that fatigue is multifactorial, and a comprehensive assessment of all potential contributing factors is essential for effective management 1, 7.