A 9-year-old boy is brought to the pediatric clinic due to facial asymmetry that began yes… — USMLE Step 2 CK

A $9$ -year-old boy is brought to the pediatric clinic due to facial asymmetry that began yesterday. The patient's mother reports he has been unusually tired and has had a low-grade fever for the past $4$ days. Exactly $3$ weeks ago, the family returned from a camping trip in Connecticut. On physical examination, temperature is $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ ), heart rate is $92\text{/min}$ , and blood pressure is $105/65\text{ mm Hg}$ . There is pronounced drooping of the right side of his face, involving both the upper and lower facial muscles. He is unable to completely close his right eye. Neurologic examination is otherwise entirely normal; there is no nuchal rigidity, photophobia, or altered mental status. Cardiovascular examination reveals a regular rhythm with no murmurs. Skin examination reveals a $7\text{-cm}$ annular erythematous plaque with central clearing on the posterior left thigh. Which of the following is the most appropriate next step in management?

Prescribe oral doxycyclineAnswer
B
Admit the patient for intravenous ceftriaxone
C
Prescribe oral acyclovir and systemic corticosteroids
D
Perform a lumbar puncture and cerebrospinal fluid analysis
E
Perform a skin biopsy of the annular lesion

Answer

Prescribe oral doxycycline

The patient's presentation of recent travel to a highly endemic area (Connecticut), fatigue, and an annular erythematous plaque with central clearing (erythema migrans) is definitively diagnostic of Lyme disease. He also presents with a unilateral facial nerve palsy (involving both the upper and lower face), which is the most common neurologic manifestation of early disseminated Lyme disease. Crucially, an isolated cranial nerve palsy in Lyme disease without clinical signs of meningitis (such as nuchal rigidity, severe headache, or photophobia) should be treated with oral antibiotics, not intravenous therapy. A

14

-day course of oral doxycycline, amoxicillin, or cefuroxime axetil is the standard treatment of choice.

Step-by-Step Solution

Identify the primary diagnosis based on the clinical presentation and physical exam findings.

The patient has a

7\text{-cm}

annular erythematous plaque with central clearing (erythema migrans) and a history of tick exposure in an endemic area (Connecticut), which clinically confirms the diagnosis of Lyme disease.

Erythema migrans is pathognomonic for Lyme disease and does not require laboratory confirmation before initiating treatment.

Categorize the stage and specific manifestations of the disease.

The patient has early disseminated Lyme disease presenting as an isolated cranial nerve VII palsy (unilateral facial droop) without any meningeal signs.

Determining the specific manifestation is crucial because the required treatment route (oral versus intravenous) depends heavily on the presence of severe neurologic or cardiac involvement.

Determine the appropriate pharmacotherapy for this specific manifestation.

Isolated facial nerve palsy without clinical signs of meningitis should be treated with oral antibiotics, specifically a

14

-day course of oral doxycycline, amoxicillin, or cefuroxime.

Unlike Lyme meningitis or severe carditis, which require intravenous ceftriaxone, isolated cranial nerve palsy responds excellently to oral therapy, effectively avoiding the risks and costs of intravenous lines.

Key Concept

Management of early disseminated Lyme disease with isolated facial nerve palsy requires oral antibiotics, not intravenous therapy.

Estimated Time:1m 15s

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