1) Fatigue is a nonspecific symptom with many causes. It refers to a sense of weariness or loss of energy that patients describe in various ways. "I don't feel like getting up in the morning"..."I don't have any energy"..."I can hardly get through the day"..."By the time I get to work, I feel as if I've done a day's work." Because fatigue is a normal response to hard work, sustained stress, or grief, elicit the life circumstances in which it occurs. Fatigue unrelated to such situations requires further investigation.

Use open-ended questions to encourage the patient to fully describe what he or she is experiencing. Important clues about etiology often energe from a good psychosocial history, exploration of sleep patterns, and a thorough review of systems.

Fatigue is a common symptom of depression and anxiety, but also consider infections (such as hepatitis, infectious mononucleosis, and tuberculosis); endocrine disorders (hypothyroidism, adrenal insufficiency, diabetes mellitus); heart failure; chronic disease of the lungs, kidneys, or liver; electrolyte imbalance; moderate to severe anemia; malignancies; nutritional deficits; and medications.

2) Weakness is different from fatigue. It denotes a demonstrable loss of muscle power and will be discussed later with other neurologic symptoms.

Weakness, especially if localized in a neuroanatomical pattern, suggests possible neuropathy or myopathy.

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