26th April 2024

A 45-year-old man, an avid hiker, presents with a 2-week history of intermittent fevers, fatigue, and a spreading rash.

A 45-year-old man, an avid hiker, presents with a 2-week history of intermittent fevers, fatigue, and a spreading rash. The rash began as a small red spot at the site of the bite and has gradually expanded, forming a characteristic “bull’s-eye” appearance. He also complains of mild headaches and joint pains. He has no past medical history of note and takes no regular medication.

On examination, his temperature is 37.9°C, pulse rate 78 bpm, and BP 125/80 mmHg. There is a 10 cm diameter erythematous rash with central clearing on his right lower leg. No neurological deficits or signs of arthritis are evident.

Which one of the following is the most likely diagnosis?