Organic causes

These include: (1,2)

• diabetes or renal disease, determined by asking about thirst, nocturia or polyuria
  
  
• fatigue is a common symptom of cardiac failure
  
  
• infections - bacterial, viral, GF, post viral, TB, HIV, Brucella, endocarditis
  
  
• iatrogenic - betablockers, antidepressants, tranquillisers, drug abuse (1)
  
  
• alcohol
  
  
• headache, which, if it is periodic and localised with visual disturbance, may be due to intracranial cause
  
  
• other endocrine:
  • hypothyroid
  • Addison's - associated GIT symptoms, postural dizziness and pigmentation
  • hypopituitary - with a history of PPH, loss of libido or amenorrhoea
    
    
• metabolic - uraemia, liver failure
  
  
• anaemia - consider a faulty diet particularly in the elderly
  
  
• myopathies e.g. myasthenia gravis
  
  
• neuropathies e.g. motor neurone disease
  
  
• malignancy

Reference

1. Hamilton W, Watson J, Round A. Investigating fatigue in primary care. BMJ. 2010 Aug 24;341:c4259.
2. Murtagh J. Fatigue - a general diagnostic approach. Australian Family Physician 2003;32(11)