Parents bring their 3-year-old son to the emergency department out of concern for his sudd… — USMLE Step 2 CK

Parents bring their 3-year-old son to the emergency department out of concern for his sudden onset of unsteadiness. According to his mother, the child began "walking like a drunk person" and falling frequently over the past 24 hours. He had a mild, unspecified febrile illness accompanied by a diffuse maculopapular rash approximately ten days prior to this presentation, which resolved completely without intervention. He has no history of head trauma and no access to medications or toxic substances. His temperature is $37.1^\circ\text{C}$ ( $98.8^\circ\text{F}$ ), blood pressure is $92/58\text{ mmHg}$ , heart rate is $105\text{/min}$ , and respiratory rate is $22\text{/min}$ . On physical examination, the child is alert, fully oriented, and interactive. Neurologic examination reveals a wide-based, staggering gait and bilateral horizontal nystagmus. He demonstrates marked dysmetria when asked to reach for a toy. Muscle tone, strength, and deep tendon reflexes are normal and symmetric in all extremities. Fundoscopic examination reveals sharp optic disc margins with no evidence of papilledema. Which of the following is the most appropriate next step in the management of this patient?

Reassurance and careful outpatient observationAnswer
B
Urgent non-contrast computed tomography of the head
C
Lumbar puncture and initiation of empiric intravenous ceftriaxone
D
Administration of oral valacyclovir therapy
E
Referral to early intervention for motor milestone delay

Answer

Reassurance and careful outpatient observation

The correct approach is reassurance and careful outpatient observation. This patient's presentation of an acute-onset wide-based gait, dysmetria, and nystagmus occurring 1 to 2 weeks after a viral illness is highly characteristic of acute cerebellar ataxia. This is a post-infectious autoimmune phenomenon that predominantly affects children aged 1 to 3 years. Because the patient is alert, afebrile, and lacks signs of increased intracranial pressure (e.g., no papilledema, no vomiting) or asymmetric focal neurologic deficits, invasive diagnostic testing or neuroimaging is not indicated. The condition is benign and typically resolves spontaneously within a few weeks, making supportive care the standard management.

Step-by-Step Solution

Analyze the core clinical presentation and timeline.

The patient is a 3-year-old with acute-onset ataxia, dysmetria, and nystagmus occurring roughly 10 days after a mild viral illness with a rash.

Establishing the sequence of events is critical for differentiating acute post-infectious processes from acute toxicologic, infectious, or structural neurologic emergencies.

Rule out life-threatening etiologies based on the physical examination.

The absence of fever, altered mental status, papilledema, and focal lateralizing neurologic signs significantly lowers the suspicion for bacterial meningitis, encephalitis, or an intracranial mass lesion (e.g., medulloblastoma).

Red flag symptoms dictate whether invasive testing or immediate neuroimaging is required.

Establish the most likely diagnosis.

The clinical picture is highly characteristic of acute cerebellar ataxia, a benign autoimmune syndrome.

Acute cerebellar ataxia is the most common cause of acute ataxia in childhood and typically follows a viral infection such as varicella, coxsackievirus, or Epstein-Barr virus.

Determine the appropriate management strategy based on the diagnosis.

Because this condition resolves spontaneously over a period of 1 to 3 weeks, supportive care and observation are the standard of care.

Unnecessary imaging or empiric medications expose the child to radiation and adverse effects without clinical benefit.

Key Concept

Diagnosis and management of post-infectious acute cerebellar ataxia

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