A 31-year-old male landscape architect seeks medical evaluation at a walk-in clinic in Rho… — USMLE Step 2 CK

A $31$ -year-old male landscape architect seeks medical evaluation at a walk-in clinic in Rhode Island during mid-July. He describes a five-day history of low-grade fevers, profound fatigue, and a spreading skin lesion on his back. Yesterday, he began experiencing difficulty holding liquids in his mouth and noticed an inability to completely shut his right eye. Vital signs are temperature $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ ), blood pressure $122/78\text{ mmHg}$ , pulse $74/\text{min}$ , and respiratory rate $14/\text{min}$ . Physical examination reveals a $12\text{ cm}$ annular, erythematous plaque with a distinct zone of central clearing on the right subscapular region. Neurologic examination demonstrates drooping of the right corner of the mouth, flattening of the right nasolabial fold, and an inability to close the right eyelid. Sensation to light touch on the face is intact. There is no nuchal rigidity, and the remainder of the examination is unremarkable. Which of the following is the most appropriate next step in management?

Prescribe a course of oral doxycyclineAnswer
B
Admit the patient for intravenous ceftriaxone therapy
C
Prescribe a course of oral cephalexin
D
Initiate therapy with oral valacyclovir and prednisone
E
Prescribe a course of oral fluconazole

Answer

Prescribe a course of oral doxycycline to treat early disseminated Lyme disease presenting with erythema migrans and an isolated facial nerve palsy.

This patient presents with a classic erythema migrans rash and a unilateral lower motor neuron facial nerve palsy, which are hallmark findings of early disseminated Lyme disease caused by the spirochete Borrelia burgdorferi. The diagnosis of Lyme disease in the presence of an erythema migrans rash is strictly clinical. For patients with Lyme disease who have an isolated facial nerve palsy (without clinical evidence of meningitis, such as nuchal rigidity, severe headache, or photophobia), oral doxycycline is the preferred treatment. Intravenous therapy is not indicated for isolated cranial neuropathies and represents poor antibiotic stewardship.

Step-by-Step Solution

Identify the primary clinical syndrome from the dermatologic and neurologic findings.

The patient has a pathognomonic erythema migrans (target-like) rash and an isolated lower motor neuron facial nerve palsy.

Recognizing erythema migrans in an endemic area establishes a definitive clinical diagnosis of Lyme disease without the need for serologic confirmation.

Determine the stage of the disease.

The presence of multiple systemic signs (rash plus cranial neuropathy) classifies this as early disseminated Lyme disease.

Staging guides the appropriate route, spectrum, and duration of antimicrobial therapy.

Select the appropriate targeted antimicrobial therapy.

Oral doxycycline is chosen because the patient has an isolated facial nerve palsy without signs of meningitis or severe carditis.

Oral therapy is highly effective for isolated cranial nerve involvement in Lyme disease, adhering to principles of good antibiotic stewardship by avoiding unnecessary intravenous broad-spectrum agents.

Key Concept

Early disseminated Lyme disease presenting with isolated facial nerve palsy should be treated with targeted oral antibiotics (e.g., doxycycline); intravenous ceftriaxone is reserved for more severe neurologic involvement such as meningitis.

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