Differential Diagnosis of Gout

Distinguishing gout from rheumatic diseases and from joint infection (septic arthritis) can sometimes be difficult – but there are clear features that help.

  1. Gout vs. Joint Infection (Septic Arthritis)

A joint infection is an acute emergency and must be treated immediately.

How to distinguish them?

🔹 Gout – Typical Features

  • Sudden onset, usually at night
  • A single joint, typically the big toe
  • Very severe pain, marked redness
  • Fever is rare or only mild
  • History of high uric acid levels, previous attacks

🔹 Infection – Typical Features

  • More pronounced general symptoms: high fever, chills, feeling severely ill
  • Joint feels extremely warm and significantly swollen
  • Often occurs after:
    • an injury
    • an operation
    • an insect bite
    • an infection elsewhere in the body
  • Inflammatory markers (CRP, leukocytes) are very high
  • Joint aspiration shows:
    • Pus-like joint fluid
    • Detection of bacteria → definitive diagnosis

 Important:
If a joint might be infected, a joint aspiration is always performed, because an untreated infection can permanently destroy the joint.

  1. Gout vs. Rheumatoid Arthritis (RA)

RA is a chronic inflammatory autoimmune disease, very different from an acute gout attack.

🔹 Gout – Typical Features

  • Acute, very severe, often nocturnal attacks
  • Usually one joint at a time
  • Commonly affected: big toe, ankle, knee
  • Between attacks: completely symptom-free
  • Long-term: tophi (urate nodules) may develop

 Rheumatoid Arthritis – Typical Features

  • Symmetrical joint inflammation
    (e.g., both finger or wrist joints)
  • Typically affects small joints of hands and feet
  • Morning stiffness lasting 30–60 minutes
  • Slow onset, not sudden like gout
  • No completely pain-free intervals
  • Blood tests:
    • Rheumatoid factor (RF) often positive
    • Anti-CCP antibodies characteristic
  1. Gout vs. Pseudogout

Pseudogout (CPPD arthropathy) resembles gout but involves different crystals.

Gout

  • Uric acid crystals (urate crystals)
  • Typically affects the big toe

Pseudogout

  • Calcium pyrophosphate crystals
  • Often affects knee or wrist
  • Crystal shape under the microscope is clearly different

Safest Method of Distinction

Joint aspiration is the gold standard:

  • Gout: needle-shaped urate crystals
  • Pseudogout: rhomboid calcium pyrophosphate crystals
  • Infection: bacteria + high cell count
  • Rheumatic diseases: no crystals, inflammatory cells

Table: Gout Attack vs. Joint Infection

Feature

Gout Attack

Joint Infection (Septic Arthritis)

Cause

Uric acid crystals

Bacteria in the joint

Onset

Very sudden, often at night

Also sudden, but usually with fever

Pain

Very severe, touch-sensitive

Extremely severe, often intolerable

Fever

Rare or mild

High fever, chills common

Affected Joint

Often big toe, single joint

Any joint, commonly knee

Appearance

Red, swollen, warm

Very warm, heavily swollen, sometimes purulent

Lab Values

Moderately elevated inflammatory markers

CRP and leukocytes markedly elevated

Uric Acid Level

Can be high or normal

Not relevant

Joint Aspiration

Needle-shaped urate crystals

Pus-like fluid + bacterial detection

Treatment

NSAIDs, colchicine, glucocorticoids

Antibiotics + joint drainage

Risk

Painful but manageable

Emergency! Joint destruction possible within hours

Summary

  • Gout: no antibiotics
  • Infection: immediate antibiotics
  • If uncertain → joint aspiration is essential