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A 3-year-old girl with an unremarkable medical history suddenly developed dilated pupils and trouble walking, according to a case report in .

The child was brought in to the emergency department the day after she developed an abnormal gait and bilateral mydriasis. "She had brisk reflexes, poor coordination, and a wide-based unsteady gait," reported Heather Stiff, MD, and colleagues at Medical College of Wisconsin, Milwaukee.

The team learned that 2 weeks previously, the patient had developed upper respiratory symptoms and an eye infection that had been identified as bacterial conjunctivitis and treated with topical ofloxacin.

On physical examination, the child's pupils were fixed and dilated to 8 mm, authors reported. She was able to move her eyes in all directions, and the fundus was normal.

Blood tests identified leukocytosis and an elevated erythrocyte sedimentation rate. Findings of blood culture examination were negative. Clinicians performed a spinal tap and results of the cerebrospinal fluid (CSF) analysis were normal, as were findings of a CT scan, and MRI scans of the brain and orbits.

Clinicians diagnosed the patient with acute cerebellar ataxia. Her energy level and walking improved over the next several days, and she was discharged 3 days later.

At the 1 -week follow-up ophthalmologic examination, Stiff and co-authors said "her visual acuity was central, steady, and maintained in both eyes." Her pupils were sluggish but reactive, suggesting that her eye muscles had weakened. "She was unable to move either eye in any direction, including with doll's head maneuver," they added.

On readmission to the hospital, she was unsteady while walking and her reflexes were less responsive on both sides of her body. The team readmitted the patient to the hospital for a follow-up MRI. This showed "diffuse enhancement of the lower thoracic and cauda equina nerve roots and enhancement of the left oculomotor nerve," they noted.

The team agreed that Miller Fisher syndrome (MFS) was the most likely diagnosis; based on this conditional diagnosis, they ordered an anti-GQ1b antibody and the patient was started on IV immune globulin.

The patient received two doses of IV immune globulin before she was discharged from the hospital. At that point, she tested positive for anti-GQ1b antibodies with a titer of 1:400.

On follow-up assessment 3 months later, she demonstrated full extraocular movements without strabismus.

Although the patient's pupils continued to be slightly dilated at 6.5 mm in darkness, they were mildly reactive, constricting to 5.5 mm with light exposure. Her visual acuity was 20/25 in the right eye, and 20/20 in the left eye.

Neurologic assessment showed that she had almost returned to her baseline functioning, and regained normal reflexes and gait.

Discussion

"[MFS] is a rare, acute, and self-limited disorder that is considered a variant of Guillain-Barré syndrome," Stiff's group wrote.

Research suggests molecular mimicry of viral components to peripheral nerve antigens as the main pathogenic mechanism. MFS is typically associated with infectious etiologies; the most common bacterial pathogen is Campylobacter jejuni, followed by Haemophilus influenzae. However, the roles of other biological factors have yet to be elucidated.

Beyond the two bacterial infections, MFS has also been reported in the setting of with Epstein-Barr virus, influenza virus, HIV, and varicella zoster virus.

In a rare case, a patient developed MFS after receiving a COVID-19 vaccination, and autoimmune and neoplastic causes have also been observed, authors noted.

Classically, MFS presents with a clinical triad of ophthalmoplegia, ataxia, and areflexia, authors noted. Although many MFS patients develop dilated pupils in both eyes, the present patient's "initial presentation with bilateral mydriasis as the only symptom has rarely been reported," Stiff and colleagues said.

Other atypical symptoms of MFS include headache, facial palsy, impaired taste, abnormally accelerated heart rate, and high blood pressure.

of MFS generally requires imaging to rule out brainstem abnormalities and compressive lesions, authors noted. Findings of a brain MRI tend to be normal or show cranial or spinal nerve root enhancement.

CSF analysis is important to confirm that symptoms are not due to an infectious etiology, they noted, adding that findings may be normal or show high protein with low white blood cell counts (albuminocytologic dissociation).

This patient had already undergone an extensive workup that included examination of blood cultures and CSF, results of which had been unrevealing. In the absence of any additional symptoms to suggest an infectious cause of the patient's symptoms, "these tests were of low utility," authors noted.

On the other hand, presence of the in the serum has an 80% to 90% sensitivity for MFS, they said. While diagnosis does not require this laboratory test, it can help narrow a diagnosis.

Because these tests may take days to weeks to be processed, Stiff and co-authors advised that patients with clinical evidence of MFS be started on IV immune globulin pending the official laboratory report.

Generally, MFS is self-limiting, has a good prognosis, and rarely recurs. "Patients are typically treated with intravenous immune globulin or, less preferably, plasmapheresis," they said. Steroids are no longer recommended, since they do not hasten recovery or demonstrated effectiveness for this condition.

Although treatment has not been proven to improve overall prognosis, "it does shorten the time to recovery compared to supportive care alone," they said.

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