18: Fatigue

CHIEF COMPLAINT

CONSTRUCTING A DIFFERENTIAL DIAGNOSIS

Before considering the differential diagnosis, it is important to understand what the patient means by fatigue, which is conventionally defined as a sensation of exhaustion after usual activities, or a feeling of insufficient energy to begin usual activities. Most people consider the terms fatigue, tiredness, and lack of energy synonymous. However, patients sometimes use these terms when they are actually experiencing other symptoms, especially excessive sleepiness, weakness, or dyspnea on exertion.

Always ask patients what they mean when they report fatigue. Always ask directly about weakness, excessive sleepiness, and dyspnea.

Acute fatigue is common in conjunction with a variety of acute illnesses, ranging from uncomplicated viral infections to exacerbations of heart failure (HF). Fatigue is also a prominent symptom in some chronic diseases, such as multiple sclerosis and cancer. This chapter will not discuss fatigue in such patients but will focus on evaluating the symptom of fatigue lasting weeks to months in patients without already diagnosed conditions known to cause fatigue.

The differential diagnosis of fatigue is extremely broad and best organized with an organ/system approach.

1. Psychiatric

   1. Depression

   2. Anxiety

   3. Somatization disorder

   4. Substance abuse

2. Sleep disorders

   1. Insomnia

   2. Obstructive sleep apnea (OSA)

   3. Periodic leg movements

   4. Narcolepsy

3. Endocrine

   1. Thyroid disease

   2. Diabetes mellitus

   3. Hypoadrenalism

4. Medications (Table 18-1)

5. Hematologic or oncologic

   1. Anemia

   2. Cancer

6. Renal: chronic kidney disease

7. Liver disease

8. Cardiovascular: chronic heart disease

9. Pulmonary: chronic lung disease

10. Neuromuscular: myositis, multiple sclerosis

11. Infectious: chronic infections

12. Rheumatologic: autoimmune diseases

13. Fatigue of unknown etiology

    1. Chronic fatigue syndrome

    2. Idiopathic chronic fatigue: fatigue for which no medical, psychiatric, or sleep pattern explanation can be found.

Figure 18-1 outlines the diagnostic approach to fatigue.

The most common causes of fatigue are psychiatric disorders, sleep disorders, and medication side effects.