About This Page
This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
The Bottom Line
- Chronic fatigue is a symptom, not a diagnosis — clarify duration, sleepiness versus weakness, exercise intolerance, mood, medication effects, substance use, and functional impact
- Red flags include involuntary weight loss, fever, night sweats, lymphadenopathy, dyspnea, chest pain, bleeding, focal neurological signs, suicidality, and rapid functional decline
- Common causes include anaemia, hypothyroidism, depression, sleep apnea, chronic pain, medication effects, alcohol/cannabis use, and chronic cardiopulmonary, renal, or liver disease
- Initial tests are targeted rather than indiscriminate: CBC, ferritin, TSH, electrolytes/creatinine, liver enzymes, glucose or HbA1c, pregnancy test where relevant, and urinalysis when indicated
- If first-line evaluation is reassuring and post-exertional malaise is prominent, consider ME/CFS or post-viral fatigue and focus on validation, pacing, sleep optimisation, and functional goals
Approach to the Presentation
Fatigue is one of the commonest constitutional presentations in Canadian primary care. The MCCQE1 approach is to separate benign, multifactorial fatigue from systemic disease that requires urgent action. Start by defining what the patient means: sleepiness, weakness, dyspnea on exertion, low motivation, cognitive fog, or exercise intolerance. Then assess time course, occupational demands, caregiving load, sleep quality, mood, menstrual and dietary history, medications, alcohol/cannabis use, infection risk, travel, cancer symptoms, and baseline versus current function. Examination should include vitals, BMI trend, conjunctival pallor, thyroid, lymph nodes, cardiopulmonary exam, abdomen, neurological screen, and mental status. The goal is a safe, staged workup that identifies treatable disease while avoiding low-yield testing cascades.
Differential Diagnosis
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Malignancy | must-not-miss | Fatigue with involuntary weight loss, fever, night sweats, persistent pain, bleeding, lymphadenopathy, or abnormal examination | CBC with differential, ferritin, age-appropriate screening review, and targeted imaging/endoscopy based on symptoms |
| Severe anaemia or marrow failure | must-not-miss | Exertional dyspnea, palpitations, pallor, syncope, pica, heavy menses, GI bleeding, bruising, recurrent infections | CBC, MCV, ferritin, B12, reticulocytes, smear; urgent assessment if severe anaemia or pancytopenia |
| Chronic infection such as HIV, TB, or endocarditis | must-not-miss | Fever, night sweats, weight loss, cough, exposure risk, injection drug use, immunosuppression, new murmur | HIV Ag/Ab, CXR/TB testing, blood cultures if febrile or endocarditis suspected |
| Adrenal insufficiency | must-not-miss | Profound fatigue, weight loss, postural dizziness, abdominal pain, hyperpigmentation, salt craving, hyponatraemia, hyperkalaemia | Morning cortisol and ACTH stimulation test; treat urgently if adrenal crisis suspected |
| Hypothyroidism | common | Cold intolerance, constipation, dry skin, weight gain, bradycardia, menorrhagia, delayed reflexes | TSH with free T4 if abnormal |
| Depression or anxiety disorder | common | Low mood, anhedonia, sleep/appetite change, poor concentration, guilt, panic symptoms, psychosocial stressors | Clinical assessment, PHQ-9/GAD-7 supportively, and suicide risk assessment |
| Sleep disorder | common | Non-restorative sleep, snoring, witnessed apnoeas, morning headache, daytime somnolence, shift work, sedatives or alcohol | STOP-Bang screening; home sleep apnea test or polysomnography when indicated |
| Medication or substance-related fatigue | common | Temporal relation with beta-blockers, sedatives, antihistamines, opioids, cannabis, alcohol, antidepressants, antipsychotics, or polypharmacy | Medication reconciliation and supervised deprescribing trial where safe |
| Chronic kidney, liver, heart, or lung disease | common | Reduced exercise tolerance, dyspnea, oedema, pruritus, jaundice, cough, orthopnea, abnormal urine | Creatinine/eGFR, urinalysis, liver enzymes, BNP/CXR/ECG if heart failure suspected, spirometry if respiratory symptoms |
| ME/CFS or post-viral fatigue syndrome | less common | Debilitating fatigue >6 months with post-exertional malaise, unrefreshing sleep, cognitive symptoms, orthostatic intolerance | Clinical diagnosis after targeted exclusion of alternative causes |
Red Flags & Key History
Symptoms
Involuntary weight loss, fever, drenching night sweats, or anorexia
Chest pain, dyspnea, syncope, or new exercise intolerance
Bleeding, melena, heavy menstrual bleeding, bruising, or recurrent infections
Suicidal ideation, psychosis, severe self-neglect, or inability to function safely
Post-exertional malaise after minimal activity
Snoring, witnessed apnoeas, morning headache, and daytime sleepiness
Recent medication change, cannabis/alcohol increase, or sedating over-the-counter medicine use
Signs
Lymphadenopathy or hepatosplenomegaly
Pallor, tachycardia, flow murmur, or orthostatic hypotension
Jaundice, ascites, peripheral oedema, clubbing, or cyanosis
Objective proximal weakness rather than subjective fatigue
Thyroid enlargement, bradycardia, delayed reflex relaxation, or dry skin
Approach to Investigation
First-line
CBC with differential + ferritinScreens for anaemia, leukocytosis, cytopenias, iron deficiency, and hematologic malignancy clues
TSHHigh-yield screen for hypothyroidism or hyperthyroidism
Electrolytes, creatinine/eGFR, liver enzymes, glucose or HbA1cAssesses renal, hepatic, metabolic, and diabetic causes
Pregnancy test where relevantImportant in reproductive-age patients with menstrual change, nausea, breast tenderness, or medication implications
UrinalysisUseful if renal disease, diabetes, infection, proteinuria, or systemic disease is suspected
Second-line
ESR/CRPUseful when inflammatory disease, infection, malignancy, polymyalgia rheumatica, or autoimmune disease is suspected
B12, folate, celiac serology, HIV, hepatitis, TB testingOrder based on dietary, GI, neurological, exposure, travel, sexual, or epidemiologic history
CXR, ECG, BNP, spirometryTargeted to respiratory or cardiac symptoms such as cough, dyspnea, orthopnea, chest pain, or reduced exercise tolerance
Specialist
Hematology referralPancytopenia, abnormal smear, persistent unexplained lymphadenopathy, or suspected marrow failure
Sleep medicine referral/testingHigh STOP-Bang, safety-sensitive occupation with somnolence, or persistent daytime impairment
Internal medicine/infectious disease referralUnexplained systemic symptoms, persistent fever, complex multisystem presentation, or high-risk exposure history
Management Principles
Choosing Wisely Canada + CFPC primary care principles1
Initial management
- Validate the symptom and quantify functional impairment across work, school, caregiving, exercise, sleep, and activities of daily living
- Address immediate red flags first: instability, severe anaemia, infection, suicidality, cancer symptoms, or cardiopulmonary symptoms
- Use a staged investigation plan rather than broad non-specific panels
- Book follow-up to review results and reassess trajectory
2
Treat identified causes
- Iron deficiency: identify source and replace iron; investigate GI bleeding when appropriate
- Hypothyroidism: levothyroxine with TSH monitoring
- Depression/anxiety: psychoeducation, psychotherapy/CBT, exercise prescription where feasible, SSRI/SNRI when indicated, and crisis planning if safety risk
- OSA: weight management, alcohol/sedative reduction, and CPAP when confirmed and appropriate
3
If no dangerous cause is found
- Explain that normal first-line tests reduce the likelihood of serious disease without dismissing the symptom
- Review sleep, activity, nutrition, alcohol/cannabis, medications, and stressors
- For post-exertional malaise, advise pacing and energy conservation rather than aggressive graded exercise escalation
- Set functional goals and reassess if new red flags emerge
4
Choosing Wisely approach
- Avoid repeated broad testing in clinically stable patients with unchanged symptoms and previously normal results
- Avoid low-yield imaging or tumour marker screening without localising features
- Use shared decision-making to explain why targeted testing is safer than indiscriminate testing
Complications & Pitfalls
- Premature psychologising: Depression and anxiety are common, but constitutional red flags must be sought before attributing fatigue to stress.
- Shotgun investigations: Broad testing without pre-test probability creates false positives and cascades.
- Missing sleep apnea: Patients may describe fatigue rather than sleepiness.
- Ignoring medication burden: Sedatives, opioids, cannabis, alcohol, and polypharmacy are frequent reversible causes.
- Failure to safety-net: Normal first-line tests do not end the process if weight loss, fever, lymphadenopathy, bleeding, or progressive decline develops.
MCCQE1 Exam Tips
- 1For chronic fatigue without red flags, the next best step is focused history/exam and targeted basic labs — not CT pan-scan or tumour markers
- 2Fatigue plus weight loss and night sweats = malignancy or chronic infection until proven otherwise
- 3Fatigue plus pallor, dyspnea, heavy menses, or melena = CBC and ferritin are high-yield first-line tests
- 4Do not diagnose ME/CFS until medical, psychiatric, medication, and sleep causes have been considered
- 5Post-exertional malaise is more specific than simple tiredness for ME/CFS-style presentations
- 6CanMEDS angle: validate symptoms, avoid unnecessary testing, explain uncertainty, and arrange follow-up
- 7In older adults, fatigue may be the presenting feature of frailty, depression, medication toxicity, occult infection, or malignancy
practicetest your knowledge on fatigue (chronic)Apply what you've learnt with MCCQE1-style questions from the iatroX Q-Bank — general & constitutional and beyond.
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