A 73-year-old man presents with 12 hours of worsening right foot pain (10/10 severity) and inability to weight-bear. He has no history of trauma.


He can never remember the names of his medical problems or his regular medications, but states he takes "water tablets" for his "heart problems".


On examination, observations are normal. The left foot and knee are non-tender, non-erythematous, with full range of motion. The right knee is unremarkable. The right foot has a large, tender, warm, erythematous mass on the 1st metatarsophalangeal joint, with the rest of the foot showing full range of motion and intact neurovascular function.

Which of the following is the most likely diagnosis?

Options:
explanation: Septic arthritis should always be on your differentials with an acute hot and swollen joint. It is a medical emergency with 10% mortality and the most serious cause of monoarthritis. If not treated urgently, the patient may develop joint damage, functional impairment, and persistent pain. The most usual sites for septic arthritis are the knee in adults and the hip in children. The patient may be pyrexial and generally unwell, although systemic symptoms occur in fewer than 50% of cases of septic arthritis, so a low clinical suspicion is required. It uncommonly presents in the metatarsophalangeal joint (2% of joints). The patient in this question is systemically well with rapid onset of symptoms and inflammation presenting in the 1st metatarsophalangeal joint. The most likely diagnosis is therefore acute gout. In practice if there were any doubt, you would take a joint aspirate and start antibiotics while awaiting the fluid analysis, microscopy, culture, and sensitivity
name: Hallux valgus
label: d
answer: no
explanation: Charcot can present with a hot, swollen, and erythematous joint. It is caused by neuropathy in the foot, most commonly as a result of poorly-controlled diabetes. The patient loses the protective sensation mechanisms which compensate for microtrauma within the feet which then leads to the destruction of the foot and ankle joints. Charcot feet are often not as painful as septic arthritis or gout, and are often painless. They don't present with raised inflammatory markers and the erythema will decrease with elevation. Septic arthritis often will present with raised inflammatory markers and the erythema will be unchanged on elevation. In this question, Charcot foot would unlikely present solely in the metatarsophalangeal joint and with such acute pain. Given the rest of the examination was unremarkable, it is unlikely that it is the cause of this patient's symptoms
name: Charcot foot
label: c
answer: no
explanation: Acute gout presents with a rapid-onset (<24hrs) hot, exquisitely tender, and swollen joint, caused by crystal inflammation from uric acid crystals depositing within the joint. 50% of all attacks and 70% of first attacks present in the first metatarsophalangeal joint. There may also be systemic upset and skin desquamation over the site. Risk factors for gout include male gender, alcohol excess, obesity, renal impairment, diabetes mellitus, and diuretics. Gout may be diagnosed without further investigations in someone with hyperuricaemia and podagra (classic acute arthritis in first metatarsophalangeal joint). If there is any doubt, then the gold standard is joint aspiration synovial fluid analysis. Diagnosis would be confirmed if monosodium urate crystals are seen on synovial fluid analysis - they show strong negative birefringence with needle-like morphology
name: Gout
label: a
answer: yes
explanation: Septic arthritis should always be on your differentials with an acute hot and swollen joint. It is a medical emergency with 10% mortality and the most serious cause of monoarthritis. If not treated urgently, the patient may develop joint damage, functional impairment, and persistent pain. The most usual sites for septic arthritis are the knee in adults and the hip in children. The patient may be pyrexial and generally unwell, although systemic symptoms occur in fewer than 50% of cases of septic arthritis, so a low clinical suspicion is required. It uncommonly presents in the metatarsophalangeal joint (2% of joints). The patient in this question is systemically well with rapid onset of symptoms and inflammation presenting in the 1st metatarsophalangeal joint. The most likely diagnosis is therefore acute gout. In practice if there were any doubt, you would take a joint aspirate and start antibiotics while awaiting the fluid analysis, microscopy, culture, and sensitivity
name: Septic arthritis
label: b
answer: no
explanation: Acute pseudogout presents similarly to gout, but with less severe pain and less commonly in the 1st metatarsophalangeal joint. It most frequently presents in the knees and wrists with an acutely inflamed, warm, erythematous, painful joint. Patients may also be pyrexial with raised inflammatory markers. Diagnosis is often made after joint aspiration showing positively birefringent rhomboid-shaped crystals
name: Acute pseudogout
label: e
answer: no

Correct answer: a

Gout

Learning point: Acute gout typically presents as sudden, severe pain and swelling in the first metatarsophalangeal joint, triggered by uric acid crystal deposition.