Approach to fatigue: Clinical sciences

Fatigue is the feeling of being mentally or physically exhausted. People experiencing fatigue may describe feeling tired, lacking energy, or being unable to carry out their usual daily tasks.

Fatigue can be caused by various conditions, which can be classified into four main groups. The first group covers conditions associated with fatigue and muscle weakness, such as hypercalcemia, hypokalemia, and neuromuscular conditions. The second one includes exertion-related fatigue, like cardiovascular and pulmonary disease. The third group covers conditions characterized by fatigue and excessive daytime sleepiness, like obstructive sleep apnea. Finally, the fourth group includes conditions characterized by generalized tiredness, like hypothyroidism, infections, depression, and myalgic encephalomyelitis.

When approaching a patient that presents with fatigue, start with a focused history and physical examination. Next, assess if your patient presents with muscle weakness. If there’s muscle weakness, your next step is to order labs, including BMP and calcium.

Let’s get started! If your patient has a history of constipation, anorexia, nausea, nephrolithiasis, bone pain, and confusion or lethargy, it's a classic presentation of hypercalcemia. This symptom combination is often summarized as 'groans, stones, bones, thrones, and psychiatric overtones'. In such cases, labs reveal a serum calcium level higher than 10.5, confirming the diagnosis.

On the other hand, your patients may report muscle cramps and palpitations. Additionally, there might be a history of chronic diarrhea or use of diuretics or laxatives. If labs reveal a serum potassium lower than 3.5, you can make a diagnosis of hypokalemia.

Here’s a clinical pearl! Mild hypokalemia is often asymptomatic, and can be easily corrected by giving oral potassium. However, severe hypokalemia, which occurs when potassium levels drop below 2.5, can lead to neuromuscular weakness and cardiac arrhythmia. In this case, be sure to correct the potassium level without delay with IV potassium to prevent heart complications! Additionally, don’t forget to order an ECG, which may reveal signs like flattened T waves, depressed ST segments, U waves, and prolonged PR or QT intervals!