Quick Answer
Gout is a compact, high-yield NEET PG cluster — pathophysiology, crystal microscopy and urate-lowering pharmacology drive most of the marks.
- Hyperuricemia — 90% underexcretion (CKD, diuretics, low-dose aspirin, alcohol, ciclosporin, ethambutol, pyrazinamide); 10% overproduction (Lesch-Nyhan HGPRT, tumour lysis, psoriasis, beer). Serum urate cut-off — 7 mg/dL men, 6 mg/dL women.
- Acute gout — podagra (first MTP), monoarthritis; needle-shaped, negatively birefringent yellow-when-parallel MSU crystals; treat with NSAIDs, colchicine, or steroids within 24 hours.
- Urate-lowering therapy — allopurinol first-line, target serum urate under 6 mg/dL (under 5 if tophi); start low, titrate up; prophylactic colchicine or NSAID for 3–6 months.
- HLA-B*5801 — Han Chinese, Thai, Korean, some Indian subgroups → SJS/TEN risk with allopurinol; screen in high-risk populations.
- Azathioprine interaction — allopurinol + febuxostat both block xanthine oxidase → life-threatening myelosuppression; reduce azathioprine to 25% or switch.
- Pseudogout — CPPD crystals — rhomboid, positively birefringent blue-when-parallel; chondrocalcinosis on X-ray; associations — hyperparathyroidism, hemochromatosis, hypomagnesaemia, hypophosphatasia.
Gout is a textbook NEET PG topic — a compact story with clear pharmacology, clear microscopy, and clear India-specific pitfalls (HLA-B*5801, ethambutol and pyrazinamide-induced hyperuricaemia, allopurinol affordability). This NEETPGAI deep dive covers the full spectrum — uric acid metabolism, acute attacks, urate-lowering therapy, tophi and renal complications, plus pseudogout and basic calcium phosphate crystal disease.
Pair this with the rheumatoid arthritis and DMARDs guide for the broader inflammatory arthritis framework.
Uric acid metabolism and hyperuricemia
The pathway
Purine bases (adenine, guanine) are catabolised via hypoxanthine → xanthine → uric acid, both terminal steps catalysed by xanthine oxidase (XO). Most mammals continue on to allantoin via uricase, but humans and other higher primates lack functional uricase — uric acid is the endpoint and accumulates.
Excretion — two-thirds renal (via URAT1 in the proximal tubule; net reabsorption), one-third gastrointestinal.
Normal serum uric acid — men under 7 mg/dL, women under 6 mg/dL (postmenopausal women approach male levels as oestrogen loss reduces uricosuria).
Causes of hyperuricemia
Overproduction (roughly 10%):
- Enzyme defects — HGPRT deficiency (complete = Lesch-Nyhan syndrome, X-linked recessive, self-mutilation + intellectual disability + choreoathetosis + hyperuricemia + gout in boys; partial = Kelley-Seegmiller); PRPP synthetase overactivity; von Gierke disease (G6Pase deficiency).
- High cell turnover — tumour lysis syndrome (post-chemotherapy in bulky tumours — high uric acid, potassium, phosphate; low calcium; AKI), chronic haemolysis, psoriasis, polycythaemia vera, myeloproliferative disease.
- Dietary and lifestyle — organ meats, seafood, alcohol (especially beer — high in guanosine), high-fructose corn syrup, sugary drinks.
Underexcretion (roughly 90%):
- Chronic kidney disease — the biggest single contributor.
- Drugs — thiazide diuretics, loop diuretics, low-dose aspirin (paradoxical — higher doses are uricosuric), ciclosporin, tacrolimus, ethambutol, pyrazinamide (both common ATT drugs — Indian exam pitfall), niacin, levodopa.
- Lead nephropathy — saturnine gout.
- Alcohol — lactic acid competes with urate at URAT1.
- Hypothyroidism, hyperparathyroidism, dehydration, obesity, metabolic syndrome.
Gout — clinical stages
Stage 1 — asymptomatic hyperuricemia
Elevated serum urate without symptoms. Most patients never develop gout; annual risk of an acute attack is around 0.5% at urate 7–8 and rises to 5% at urate above 9. Not treated unless very high (over 9) with additional risk factors or planned tumour lysis chemotherapy.
Stage 2 — acute gouty arthritis
Sudden onset over hours; peak severity within 24 hours; explosive erythema, swelling and exquisite tenderness (the classic patient can't tolerate a bedsheet over the toe).
Distribution — 50% of first attacks are podagra (first metatarsophalangeal joint) — the classic image in every question bank; midfoot, ankle, knee, wrist and finger joints follow. Polyarticular presentation is more common in women, elderly, and long-standing untreated disease.
Triggers — alcohol binge (beer worst), protein-rich meal, surgery, trauma, dehydration, starting or stopping urate-lowering therapy, diuretic initiation.
Synovial fluid — needle-shaped monosodium urate (MSU) crystals, intracellular in neutrophils; strongly negatively birefringent — yellow when parallel to the slow axis of the polariser, blue when perpendicular. Inflammatory count (10,000 to 50,000 WBC/microlitre, neutrophil predominant); always send for Gram stain and culture to exclude septic arthritis, which can coexist.
Stage 3 — intercritical gout
Symptom-free interval between attacks — the window for prevention. Even between flares, MSU crystals persist in synovium and imaging can show deposition.
Stage 4 — chronic tophaceous gout
Chronic, often polyarticular disease with tophi — palpable urate deposits at:
- Ear helix.
- Olecranon bursa.
- Achilles tendon.
- Finger DIP joints.
- Kidney (urate nephropathy, uric acid stones).
Radiograph — punched-out juxta-articular erosions with overhanging edges ("rat-bite" erosions) and preserved joint space until late; distinguishes chronic gout from RA (which shows marginal erosions and juxta-articular osteopenia).
Renal manifestations
- Uric acid kidney stones — approximately 10% of all renal stones; radiolucent on plain X-ray; visible on CT and ultrasound; treatment includes urine alkalinisation with potassium citrate (dissolves uric acid stones) plus allopurinol.
- Chronic urate nephropathy — interstitial urate deposition; contributes to CKD in longstanding disease.
- Acute urate nephropathy — in tumour lysis syndrome — massive urate load precipitates in tubules → AKI. Prevention with hydration, allopurinol or rasburicase (recombinant uricase).
Acute gout attack — management
Start therapy within 24 hours of onset. Three first-line options — pick based on comorbidities.
| Option | Regimen | Watch-outs |
|---|
| NSAIDs | Naproxen 500 mg BD; indomethacin 50 mg TDS; ibuprofen | Avoid CKD, PUD, uncontrolled HTN, CHF, warfarin, elderly |
| Colchicine | 1.2 mg PO, then 0.6 mg 1 hour later, then 0.6 mg once or twice daily until resolution | Avoid CKD, hepatic impairment, and with strong CYP3A4/P-gp inhibitors (clarithromycin, ciclosporin, PIs); GI intolerance |
| Oral glucocorticoids | Prednisolone 30–40 mg OD × 5–7 days | Useful when NSAIDs and colchicine contraindicated; hyperglycaemia |
| Intra-articular glucocorticoid | Single accessible joint | Rule out septic arthritis first |
| IL-1 inhibitor (anakinra, canakinumab) | Refractory or contraindications | Cost; infection risk |
- Ice + rest.
- Never start or stop ULT during an acute attack — continue if already on; do not initiate mid-flare (mobilisation flare risk).
Urate-lowering therapy (ULT)
Indications (2020 ACR — strongly recommended)
- Two or more flares per year.
- Any tophus (visible or imaging).
- Radiographic gouty damage.
- Urolithiasis or urate nephropathy.
Conditionally recommended after even a single flare when:
- CKD stage 3 or worse.
- Serum urate above 9 mg/dL.
- Urolithiasis.
Target serum uric acid
- Under 6 mg/dL for most patients.
- Under 5 mg/dL for those with tophi (encourages tophi dissolution).
The drugs
| Drug | Mechanism | Key notes |
|---|
| Allopurinol | Xanthine oxidase inhibitor | First-line. Start 100 mg/day (50 mg if eGFR under 60); titrate every 2–5 weeks. HLA-B*5801 testing in high-risk populations to reduce SJS/TEN. Reduce azathioprine to 25%. Increased maculopapular rash with amoxicillin. Increases warfarin INR |
| Febuxostat | Non-purine XO inhibitor | Alternative for allopurinol intolerance or renal impairment (no dose adjustment for mild-moderate CKD). CARES trial — increased cardiovascular death vs allopurinol; use cautiously in CV disease. Hepatotoxicity — monitor LFTs. Same azathioprine interaction |
| Probenecid | Uricosuric (URAT1 inhibitor) | Avoid in CKD (eGFR under 50) and urate kidney stones. Alkalinise urine + hydrate |
| Benzbromarone | Uricosuric | Not widely available; hepatotoxicity |
| Pegloticase | Recombinant pegylated uricase | Refractory tophaceous gout; IV infusion; anti-drug antibodies limit response; check G6PD (haemolysis) |
Prophylaxis during ULT initiation
Start colchicine 0.6 mg once or twice daily or low-dose NSAID and continue for at least 3–6 months while ULT is being uptitrated — prevents mobilisation flares as urate crystals dissolve.
Diet and lifestyle
- Reduce alcohol (especially beer), organ meats and seafood; limit sugary drinks and high-fructose corn syrup.
- Dairy — protective (low-fat milk and yoghurt reduce urate).
- Cherries — modest evidence of reducing flares.
- Coffee — protective.
- Adequate hydration.
- Weight loss (gradual — crash diets can precipitate attacks).
Pseudogout and CPPD deposition disease
Calcium pyrophosphate dihydrate (CPPD) crystal deposition in cartilage. Multiple clinical presentations.
Clinical patterns
- Acute CPP crystal arthritis (pseudogout) — acute mono- or oligoarthritis; knee, wrist (radiocarpal), MCP most common; triggered by trauma, surgery, hospitalisation, metabolic derangement.
- Osteoarthritis with CPPD — accelerated or unusual-distribution OA (e.g., wrist, MCP — usually spared in primary OA).
- Chronic CPP inflammatory arthritis — chronic polyarticular pattern mimicking RA.
- Crowned dens syndrome — cervical spine involvement.
Diagnosis
- Synovial fluid polarised microscopy — rhomboid or rod-shaped, positively birefringent CPPD crystals; blue when parallel to slow axis, yellow when perpendicular.
- Radiograph — chondrocalcinosis (linear calcification of hyaline and fibrocartilage — knee menisci, triangular fibrocartilage of wrist, symphysis pubis).
Secondary CPPD associations (screen if young or atypical)
Mnemonic — "HHHH" — Hyperparathyroidism, Hemochromatosis, Hypomagnesaemia, Hypophosphatasia. Also Wilson disease. Check calcium, phosphate, magnesium, ferritin, iron studies, PTH.
Treatment
- Acute — same as acute gout — NSAIDs, colchicine, intra-articular steroid, oral steroid.
- Chronic prophylaxis — colchicine 0.6 mg daily, low-dose NSAID.
- Treat underlying — parathyroidectomy for hyperparathyroidism, phlebotomy for hemochromatosis, magnesium replacement.
Basic calcium phosphate (hydroxyapatite) disease
Deposition of calcium hydroxyapatite crystals — very small, not visible on standard polarised microscopy; alizarin red staining reveals them.
- Calcific tendinitis — supraspinatus most common; acute severe shoulder pain.
- Milwaukee shoulder — destructive shoulder arthropathy in elderly women; large effusion, rotator cuff tear, complete cartilage loss; hydroxyapatite crystals in aspirate.
- Treatment — supportive; steroid injection; surgery for refractory rotator cuff.
Calcium oxalate arthropathy
Rare — end-stage renal disease on dialysis (primary hyperoxaluria types 1 and 2, or secondary oxalate accumulation). Bipyramidal ("envelope-shaped") crystals — similar to urinary oxalate stones.
NEET PG MCQ traps
- Podagra — first MTP joint gout; 50% of first attacks.
- MSU crystals — needle-shaped, negatively birefringent, yellow parallel to slow axis.
- CPPD crystals — rhomboid, positively birefringent, blue parallel to slow axis.
- Chondrocalcinosis — X-ray finding of pseudogout; classic in meniscus of knee.
- Lesch-Nyhan — X-linked HGPRT deficiency; self-mutilation + choreoathetosis + gout in boys.
- Tumour lysis syndrome — hyperuricaemia + hyperkalaemia + hyperphosphataemia + hypocalcaemia + AKI; prevent with hydration + allopurinol or rasburicase.
- Rasburicase — recombinant uricase; contraindicated in G6PD deficiency (severe haemolysis).
- Uric acid stones — radiolucent on plain X-ray; visible on CT; treat with urine alkalinisation (potassium citrate) + allopurinol.
- Tophi on X-ray — punched-out juxta-articular erosions with overhanging edges (rat-bite).
- Serum urate target — under 6 mg/dL, or under 5 with tophi.
- HLA-B*5801 — screen in Han Chinese, Thai, Korean, some Indian populations before allopurinol.
- Allopurinol + azathioprine — reduce azathioprine to 25% or switch (xanthine oxidase inhibition → 6-MP accumulation → myelosuppression).
- Allopurinol + amoxicillin — increased rash.
- Febuxostat CARES trial — cardiovascular death signal; caution in CV disease.
- Probenecid — avoid in CKD (eGFR under 50) and urate stones.
- Colchicine + clarithromycin / ciclosporin — toxic accumulation; avoid.
- Prophylaxis during ULT — colchicine or low-dose NSAID for 3–6 months to prevent mobilisation flares.
- Never start ULT during acute attack; continue if already on.
- Secondary CPPD — hyperparathyroidism, hemochromatosis, hypomagnesaemia, hypophosphatasia.
- Milwaukee shoulder — elderly women, hydroxyapatite crystals, destructive shoulder arthropathy.
India context
- Rising incidence — dietary transition, obesity, metabolic syndrome and increased longevity are pushing gout prevalence up; still under-diagnosed and often mislabelled as "arthritis" in primary care.
- HLA-B*5801 — the SJS/TEN-risk allele; frequency varies by region within India, with higher prevalence reported in some populations. Screening before allopurinol initiation is recommended by international guidelines and increasingly discussed in Indian rheumatology practice — though implementation is not yet routine.
- Ethambutol + pyrazinamide in NTEP anti-TB therapy raises serum urate — usually asymptomatic; frank gout uncommon but a favourite exam question.
- Allopurinol — cheapest and most widely available ULT in India; the first-line choice by cost and evidence.
- Febuxostat — increasingly used, particularly in CKD; watch cardiovascular risk profile.
- Pegloticase — expensive and limited availability; refractory tophaceous cases only.
- Beer and alcohol counselling — key primary care intervention.
- Dietary counselling — culturally adapted; reduce organ meats (kaleji, etc.), seafood, alcohol; emphasise low-fat dairy and hydration.
- Renal calculus screening — imaging (ultrasound or non-contrast CT) in patients with recurrent renal colic and hyperuricaemia.
Frequently asked questions
How do you differentiate an acute gout attack from pseudogout on synovial-fluid analysis?
Both cause acute crystal arthritis and both present with inflammatory joint fluid (typically 10,000 to 50,000 WBC/microlitre, neutrophil predominant). The key distinction is polarised light microscopy of the synovial aspirate. Monosodium urate (MSU) crystals of gout are needle-shaped and strongly negatively birefringent — they appear yellow when their long axis is parallel to the slow axis (the axis of the red compensator) and blue when perpendicular. Calcium pyrophosphate dihydrate (CPPD) crystals of pseudogout are rhomboid or rod-shaped and weakly positively birefringent — blue when parallel to the slow axis and yellow when perpendicular. Joint distribution differs too: gout classically hits the first MTP joint (podagra), midfoot, ankle and knee; pseudogout preferentially affects the knee, wrist (radiocarpal) and MCP joints, often on a background of chondrocalcinosis (linear calcification of hyaline or fibrocartilage) on plain radiographs.
What is the current stepwise management of an acute gout attack?
The 2020 ACR guideline recommends starting therapy within 24 hours of attack onset. Three first-line options with equivalent efficacy — choice depends on comorbidities. (1) NSAIDs — naproxen 500 mg twice daily, indomethacin 50 mg three times daily, or ibuprofen; avoid in CKD (eGFR less than 30), peptic ulcer disease, uncontrolled hypertension, congestive heart failure, and warfarin. (2) Colchicine — 1.2 mg orally followed by 0.6 mg one hour later, then 0.6 mg once or twice daily until resolution; avoid in CKD, hepatic impairment, and with strong CYP3A4 or P-gp inhibitors (clarithromycin, ciclosporin, HIV protease inhibitors); GI side effects are the main issue. (3) Oral glucocorticoids — prednisolone 30 to 40 mg daily for 5 to 7 days; useful when NSAIDs and colchicine are contraindicated. Intra-articular steroid is excellent for a single accessible joint. Adjunctive ice and rest help. IL-1 inhibitors (anakinra, canakinumab) are reserved for refractory attacks. Never start or stop urate-lowering therapy during an acute attack — continue if already on, don't initiate mid-flare.
When should urate-lowering therapy be started and what is the target serum uric acid?
The 2020 ACR guideline strongly recommends urate-lowering therapy (ULT) for any patient with two or more gout flares per year, tophi (visible or on imaging), radiographic damage attributable to gout, or urate nephropathy or renal calculi. It is conditionally recommended after even a single flare in patients with CKD stage 3 or worse, very high serum uric acid (over 9 mg/dL), or urolithiasis. Allopurinol is first-line — start low at 100 mg per day (50 mg per day if eGFR under 60), titrate up every 2 to 5 weeks to achieve serum uric acid under 6 mg/dL, or under 5 if tophi are present. HLA-B*5801 testing before allopurinol is recommended in high-risk populations — Han Chinese, Thai, Korean and some Indian subgroups — because of the increased Stevens-Johnson syndrome and toxic epidermal necrolysis risk in carriers. Add anti-inflammatory prophylaxis (colchicine 0.6 mg once or twice daily, or low-dose NSAID) for at least 3 to 6 months during ULT initiation to prevent mobilisation flares.
What are the key drug interactions and safety concerns with allopurinol and febuxostat?
Allopurinol — (1) allopurinol hypersensitivity syndrome (AHS) — a life-threatening DRESS-like reaction with rash, fever, eosinophilia and multi-organ involvement; risk highest in HLA-B5801 carriers and in CKD; mortality up to 25 percent. Start low, titrate slowly, screen HLA-B5801 in high-risk populations. (2) Azathioprine and 6-mercaptopurine — allopurinol inhibits xanthine oxidase which metabolises these thiopurines, causing life-threatening myelosuppression; reduce azathioprine to 25 percent of the usual dose or use an alternative ULT. (3) Warfarin — increased INR; monitor. (4) Amoxicillin — increased maculopapular rash risk. Febuxostat — (1) Cardiovascular signal from the CARES trial showed higher cardiovascular death vs allopurinol in patients with established cardiovascular disease; use cautiously and consider allopurinol first in patients with CV disease. (2) Hepatotoxicity — monitor LFTs. (3) Same azathioprine and 6-MP interaction as allopurinol — do not co-administer. (4) No HLA-B*5801 concern — an alternative in confirmed carriers.
Which primary conditions cause secondary hyperuricemia and gout?
Hyperuricemia is either overproduction (10 percent of cases) or underexcretion (90 percent). Overproduction causes — (1) enzyme deficiencies such as HGPRT deficiency (complete = Lesch-Nyhan with self-mutilation, intellectual disability and early gout in boys; partial = Kelley-Seegmiller); PRPP synthetase overactivity; von Gierke disease (glucose-6-phosphatase). (2) High cell turnover — tumour lysis syndrome, chronic haemolysis, psoriasis, polycythaemia vera. (3) High purine intake — organ meats, seafood, alcohol especially beer, high-fructose corn syrup. Underexcretion causes — (1) CKD — the biggest single factor. (2) Drugs — thiazide and loop diuretics, low-dose aspirin (paradoxically uricosuric at higher doses), ciclosporin, tacrolimus, ethambutol, pyrazinamide, niacin, levodopa. (3) Lead nephropathy — saturnine gout. (4) Alcohol — lactic acid competes with urate at the tubular transporter; beer is worst (also high in purines). (5) Hypothyroidism, hyperparathyroidism, dehydration.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team
Reviewed by: Pending SME Review
Last reviewed: July 2026
