Fatigue is a common yet complex symptom encountered in clinical practice, affecting patients across a wide spectrum of medical conditions. It is characterized by a persistent sense of tiredness or lack of energy that is not relieved by rest, and it can significantly impair a patient’s quality of life.
For doctors, understanding the underlying causes of fatigue and distinguishing between acute and chronic presentations is crucial in delivering appropriate care.

Potential Causes to Consider

Fatigue is a common yet complex symptom encountered in clinical practice, affecting patients across a wide spectrum of medical conditions.
It is characterized by a persistent sense of tiredness or lack of energy that is not relieved by rest, and it can significantly impair a patient’s quality of life.
For doctors, understanding the underlying causes of fatigue and distinguishing between acute and chronic presentations is crucial in delivering appropriate care.

🔎 Potential Causes to Consider

⚠️ Cause	📖 Details	🧪 Tests	💊 Management
🩸 Anaemia	Low Hb from iron, B12, folate deficiency or chronic disease → pallor, SOB, dizziness	CBC, Iron studies, B12/Folate, Blood film	Iron / B12 supplements, treat underlying cause
🦋 Hypothyroidism	Low thyroid hormones → weight gain, cold intolerance, constipation	TSH, Free T4	Levothyroxine replacement
😴 Chronic Fatigue Syndrome (CFS)	Unexplained fatigue >6 months + muscle aches, cognitive “brain fog”	Diagnosis of exclusion, bloods, sleep studies	CBT, graded exercise, supportive therapy
🧠 Depression	Low mood, poor motivation, sleep/appetite disturbance	Psych history, PHQ-9	SSRIs/SNRIs, CBT, lifestyle support
😴 Sleep Apnoea	Obstructed sleep → snoring, daytime drowsiness, poor concentration	Polysomnography (sleep study)	CPAP, weight loss, surgery if severe
🍬 Diabetes Mellitus	Fatigue from hyper/hypoglycaemia → polyuria, polydipsia, blurred vision	Fasting glucose, HbA1c	Glycaemic control with insulin/orals + lifestyle
🦠 Infections (e.g. Mono, HIV)	Immune activation → fever, lymphadenopathy, myalgia	Viral serology, CBC (lymphocytosis)	Rest, hydration, antivirals (HIV), symptomatic relief
🎗️ Malignancy	Cancer-related fatigue → weight loss, sweats, persistent pain	CBC, tumour markers, CT/MRI, biopsy	Oncological therapy + supportive care
❤️ Heart Failure	Low cardiac output → dyspnoea, edema, orthopnoea	Echocardiogram, BNP, CXR	Diuretics, ACEi, beta-blockers, lifestyle

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Causes of Fatigue

Introduction

Potential Causes to Consider

🔎 Potential Causes to Consider

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