Priority Topic: Fatigue

Key Feature 1: In all patients complaining of fatigue, include depression in the differential diagnosis. 
Skill: Clinical reasoning
Phase: Hypothesis generation

Key Feature 3: Exclude adverse effects of medication as the cause in all patients complaining of fatigue.
Skill: Clinical Reasoning
Phase: Hypothesis generation, Diagnosis

A 39 year old female presented to clinic today for a breast lump. On review of systems, she noted feeling fatigued for 4-6 months or so. Later in the day, a 51 year old male presented for a periodic health examination and noted being more fatigued than before, also for many months.

My DDx (per LMCC Objectives) for a complaint of fatigue is as follows:

1. Pharmacologic
   1. Hypnotic
   2. Antihypertensives
   3. Antidepressants
   4. Substance abuse
2. Disease categories associated with fatigue
   1. Infectious
   2. Neoplastic-hematologic
   3. Cardiopulmonary
   4. Endocrine-metabolic
   5. Connective tissue disorders
   6. Sleep disturbances (ex: shift work)
   7. Psychiatric
3. Idiopathic
   1. Fibromyalgia
   2. Chronic fatigue syndrome
   3. Idiopathic chronic fatigue 

What kind of DDx has multiple organ systems as a single item on the differential? Fatigue is a hell of a presenting complaint. 

On review of my patients' systems, they both described that their mood was lower in the past few months than it usually has been. But is this a chicken or egg? While both patients endorsed an associated psychiatric symptom, low mood can also be secondary to underlying disease. So just like the diagnosis of any psychiatric condition first requires us to rule out any general medical condition that could be the etiology underlying the presentation, we must hold the presenting complaint of fatigue to the same standards, however somatizing the presentation may appear.