A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 62-year-old man comes to the physician because of painless swelling in his left foot for 4 months. The swelling was initially accompanied by redness, which has since resolved. He has not had fever or chills. He has a history of coronary artery disease, hyperlipidemia, and type 2 diabetes mellitus. He has had 3 sexual partners over the past year and uses condoms inconsistently. His mother had rheumatoid arthritis. Current medications include clopidogrel, aspirin, metoprolol, losartan, atorvastatin, and insulin. He is 180 cm (5 ft 11 in) tall and weighs 95 kg (209 lb); BMI is 29 kg/m2. Vital signs are within normal limits. Cardiovascular examination shows no abnormalities. Examination of the feet shows swelling of the left ankle with collapse of the midfoot arch and prominent malleoli. There is no redness or warmth. There is a small, dry ulcer on the left plantar surface of the 2nd metatarsal. Monofilament testing shows decreased sensation along both feet up to the shins bilaterally. His gait is normal. Which of the following is the most likely diagnosis?
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A
Calcium pyrophosphate arthropathyIncorrect. CPPD arthropathy (pseudogout) typically affects knees and wrists with episodic painful flares and chondrocalcinosis on x-ray, not painless midfoot collapse with neuropathy.
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B
Tertiary syphilisIncorrect. Tertiary syphilis can cause tabes dorsalis with Charcot joints, but the joints affected are usually large weight-bearing ones (knee), and there would typically be other neurosyphilis signs (Argyll Robertson pupils, ataxia); diabetic neuropathy is the far more common etiology here.
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C
Reactive arthritisIncorrect. Reactive arthritis presents days to weeks after GU or GI infection with asymmetric oligoarthritis, conjunctivitis, and urethritis — not painless chronic midfoot collapse with peripheral neuropathy.
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D
Diabetic arthropathyCorrect. painless midfoot deformity with arch collapse, sensory neuropathy, and plantar ulcer in a long-standing diabetic is the classic Charcot diabetic arthropathy.
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E
GoutIncorrect. Gout (monosodium urate crystal arthropathy) presents with acute, exquisitely painful monoarthritis, classically of the first MTP joint, with negatively birefringent needle-shaped crystals — not painless midfoot collapse with neuropathy and plantar ulcer.
↑ Tap an answer to reveal the reasoning
Answer: D. Painless midfoot deformity with collapse of the longitudinal arch ('rocker-bottom foot'), bony prominence of the malleoli, a plantar ulcer, and decreased monofilament sensation up to the shins in a diabetic patient is Charcot neuroarthropathy — also called diabetic arthropathy. The pathogenesis combines two insults: (1) peripheral sensory neuropathy that blunts protective pain feedback, allowing repetitive microtrauma to go unnoticed, and (2) autonomic neuropathy with increased bone blood flow and osteoclast activation, leading to bone resorption and fragmentation. The result is progressive joint destruction, dislocation, and the classic midfoot collapse.
The initial inflammatory phase (warm, swollen, erythematous foot) often mimics cellulitis or osteomyelitis but is sterile; this patient's erythema has already resolved, leaving the chronic deformity. The plantar ulcer reflects loss of normal foot architecture and abnormal pressure distribution.
Clinical pearl: management is non–weight-bearing in a total contact cast for several months to halt progression. Charcot foot must be distinguished from osteomyelitis (especially with an overlying ulcer) — MRI and sometimes bone biopsy may be needed.
**Why each option:**
**A.** CPPD arthropathy (pseudogout) typically affects knees and wrists with episodic painful flares and chondrocalcinosis on x-ray, not painless midfoot collapse with neuropathy.
**B.** Tertiary syphilis can cause tabes dorsalis with Charcot joints, but the joints affected are usually large weight-bearing ones (knee), and there would typically be other neurosyphilis signs (Argyll Robertson pupils, ataxia); diabetic neuropathy is the far more common etiology here.
**C.** Reactive arthritis presents days to weeks after GU or GI infection with asymmetric oligoarthritis, conjunctivitis, and urethritis — not painless chronic midfoot collapse with peripheral neuropathy.
**D.** Correct — painless midfoot deformity with arch collapse, sensory neuropathy, and plantar ulcer in a long-standing diabetic is the classic Charcot diabetic arthropathy.