Published: 27 Oct 2024

A differential diagnosis is a systematic method doctors use to identify the possible conditions that might be causing a patient's symptoms.
This process is especially useful when symptoms are non-specific or can stem from a range of different conditions, rather than a single clear cause. Here's an outline of common symptoms that often require differential diagnosis, along with examples of possible causes for each:

1. Fever of Unknown Origin (FUO)
- Possible Causes: Infection (bacterial, viral, fungal, or parasitic), autoimmune diseases (lupus, rheumatoid arthritis), cancers (leukemia, lymphoma), and inflammatory conditions.
- Approach: Investigate travel history, recent exposures, and consider rare infections or atypical presentations of common conditions.

2. Unexplained Fatigue
- Possible Causes: Anemia, hypothyroidism, depression, chronic fatigue syndrome, sleep apnea, autoimmune disorders, and even certain infections like mononucleosis.
- Approach: Check blood count, thyroid function tests, and consider mental health screening or sleep study, depending on the presentation.

3. Chronic Pain (especially musculoskeletal)
- Possible Causes: Fibromyalgia, rheumatoid arthritis, osteoarthritis, muscle strain, and nerve-related issues (e.g., sciatica).
- Approach: Consider imaging for structural issues, labs for autoimmune markers, and thorough pain assessment.

4. Shortness of Breath
- Possible Causes: Heart conditions (heart failure, coronary artery disease), lung issues (COPD, asthma, pulmonary embolism), anemia, and anxiety disorders.
- Approach: Imaging (chest X-ray or CT), oxygen saturation, pulmonary function tests, and ECG, as well as D-dimer for suspected clotting issues.

5. Abdominal Pain
- Possible Causes: Gastrointestinal issues (appendicitis, gallstones, irritable bowel syndrome), urinary problems (UTI, kidney stones), gynecologic issues (ovarian cyst, endometriosis), and even referred pain from cardiac or lung issues.
- Approach: Physical exam, abdominal imaging, blood tests (CBC, liver function), and possibly urine tests or gynecological exam.

6. Headache
- Possible Causes: Migraine, tension headache, cluster headache, sinus infection, meningitis, or even less common causes like brain tumor or aneurysm.
- Approach: Detailed history to assess patterns, severity, triggers, and imaging if red flags like sudden-onset headache or neurological symptoms are present.

7. Dizziness
- Possible Causes: Vertigo (inner ear issues), anemia, dehydration, hypoglycemia, medication side effects, or cardiac arrhythmias.
- Approach: Check for signs of inner ear issues, blood pressure, blood sugar, and review medications, with further testing like an ECG or balance tests if needed.

8. Weight Loss without Intent
- Possible Causes: Malignancy, hyperthyroidism, diabetes, gastrointestinal issues (e.g., celiac disease), or even chronic infections like HIV or TB.
- Approach: Blood tests (thyroid function, blood sugar), imaging for possible malignancies, and consideration of recent infections or gastrointestinal symptoms.

9. Chest Pain
- Possible Causes: Cardiovascular issues (angina, myocardial infarction), musculoskeletal causes (costochondritis), gastrointestinal reflux, and anxiety or panic disorders.
- Approach: ECG, blood tests for cardiac enzymes, chest X-ray, and if cardiac causes are ruled out, consider gastrointestinal or musculoskeletal evaluation.

10. Joint Pain and Swelling
- Possible Causes: Rheumatoid arthritis, lupus, osteoarthritis, gout, or septic arthritis.
- Approach: Blood tests for inflammatory markers, uric acid for gout, joint imaging, and possibly joint fluid analysis for infection.

Key Considerations in Differential Diagnosis
- Patient History: A thorough history is essential. Travel history, family medical history, medications, and lifestyle factors can provide vital clues.
- Physical Examination: A careful physical exam can often narrow down the possible causes.
- Lab Tests & Imaging: Targeted testing based on the leading possible causes is typically employed to help rule in or rule out specific conditions.

Differential diagnosis is a cornerstone of effective medicine because it accounts for complexity in presentation and prevents misdiagnosis. Use DDxHub.com online tool to run differential diagnosis.