Chapter 16: Fatigue Assessment & Differential Diagnosis

The text distinguishes between physiological fatigue, often caused by overwork or lifestyle factors, and psychological fatigue, which is frequently linked to stress, anxiety, or depression. It further categorizes the condition into acute fatigue, lasting (lesser than) six months and often serving as a prodrome to infections like endocarditis or hepatitis, and chronic fatigue, which persists longer than six months and requires investigating systemic diseases or chronic fatigue syndrome (CFS). A thorough diagnostic reasoning process is outlined, emphasizing the importance of distinguishing true fatigue from muscle weakness or frailty, particularly in older adults where frailty encompasses weight loss, slow mobility, and reduced activity. The chapter details the necessity of a focused history taking that evaluates sleep patterns, nutritional habits, medication side effects, substance use, and occupational exposures to toxins or heavy metals. The physical examination section guides clinicians to assess general appearance for signs of neglect or distress, check vital signs for hemodynamic stability, and inspect the skin, thyroid, cardiovascular, and musculoskeletal systems for organic clues such as hypothyroidism, heart failure, or the tender points associated with fibromyalgia. Critical laboratory and diagnostic studies are reviewed, including the Complete Blood Count (CBC) with indices to identify microcytic or normocytic anemia, ferritin levels for iron stores, TSH for thyroid dysfunction, and glucose testing for diabetes and prediabetes. The text also covers infectious disease screenings for HIV, tuberculosis, and mononucleosis. Finally, the chapter provides an extensive differential diagnosis breakdown, contrasting physiological causes like poor sleep hygiene and nutritional deficits with organic causes such as sleep apnea, malignancies, and autoimmune disorders, while outlining the specific clinical criteria required to diagnose Chronic Fatigue Syndrome and fibromyalgia in a primary care setting.