Approach to ankle pain Quiz: Ace Your Exams

A 68-year-old man presents to the primary care clinic for evaluation of right ankle pain that has progressively worsened over the past three weeks. He describes the pain as deep and constant and that it is occasionally sharp. He has not had recent trauma. He reports intermittent fevers, chills, and night sweats. He also notes increased swelling and redness over the right ankle over the past week. The patient has a history of poorly controlled type 2 diabetes with a recent HbA1c of 9.2%. Temperature is 38.1°C (100.6°F), pulse is 94/min, respiratory rate is 16/min, blood pressure is 126/84 mmHg, and oxygen saturation is 99% on room air. The right ankle is erythematous, swollen, and tender to palpation with noticeable warmth. There is a small, non-healing ulcer on the plantar surface of the forefoot. There is a reduced range of motion of the foot due to pain, but there is no crepitus or obvious deformity. Pedal pulses are present but diminished. There is decreased sensation to light touch and pinprick over the right foot and toes. Examination of the left foot reveals decreased sensation to light touch and pinprick but is otherwise normal. An X-ray of the ankle shows a lucent area in the distal tibia with surrounding periosteal reaction and no other bony deformities. Examination of the left foot and ankle is within normal limits. Laboratory results are shown below. Which of the following is the most likely diagnosis?

Laboratory Value	Result	Reference Range
Leukocyte count	15,000/µL	4,6500-11,000/µL
Erythrocyte sedimentation rate (ESR)	50 mm/hr	0-15 mm/hr
C-reactive protein (CRP)	45 mg/L	<0.3 mg/L