**Background:** Miller Fisher syndrome (MFS) is a rare variant of Guillain-Barré syndrome (GBS) characterized by the triad of ataxia, ophthalmoparesis, and areflexia. The worldwide incidence of GBS is approximately 1-2 per 100,000, with MFS representing about 5% of GBS cases. Since the onset of the COVID-19 pandemic, numerous reports of peripheral and central nervous system involvement have emerged. By December 2022, 24 cases of COVID-19-associated MFS had been reported, including only two children. This paper presents the third pediatric case and the youngest reported to date—a 6-year-old boy with MFS following mild COVID-19 infection.
**Methods:** The patient was a 6-year-old male who developed sore throat, nasal discharge, and fatigue 12 days prior to presentation. Subsequently, he experienced double vision, imbalance, and limitation of eye movements over a few days. He was evaluated by an ophthalmologist, pediatrician, and neurologist. On neurological examination, he was fully alert and oriented. Visual acuity was 6/6 bilaterally, color vision was normal, and visual fields were intact. He had bilaterally dilated pupils with a weak response to light. Ocular movements were paretic in all directions, with inability to maintain saccadic eye movements, especially horizontally. Left ptosis was present. Anterior segment and fundoscopy were normal. Deep tendon reflexes were absent in all limbs. He displayed significant dysmetria on finger-to-nose testing, ataxic gait, and a positive Romberg test. Brain MRI was normal. A COVID-19 test was positive at the onset of symptoms and remained positive on repeat testing. Nerve conduction studies showed normal motor responses but reduced sensory nerve action potential (SNAP) amplitudes in all four extremities. F-wave latencies could not be obtained from both tibial nerves, and ulnar F-wave latency was prolonged. H-reflex responses were absent. Cerebrospinal fluid (CSF) analysis revealed albuminocytologic dissociation (ACD) with a protein level of 87 mg/dL (normal 15-45 mg/dL), no cells, and negative Gram stain and culture. Anti-GQ1b IgG and IgM antibodies were negative (<1700 BTU). Autoimmune and vasculitic panels were negative. The patient was monitored without immunotherapy and showed significant improvement after one week, with near-complete recovery by the end of three months.
**Key Results:** This is the youngest reported case of COVID-19-associated MFS (6 years old) and the third pediatric case. The patient had mild COVID-19 symptoms. Anti-GQ1b antibodies were negative, but CSF showed ACD (protein 87 mg/dL). Electrophysiological findings included reduced SNAP amplitudes, absent H-reflexes, and prolonged or absent F-waves. The patient recovered spontaneously without IVIg or plasma exchange. A review of the literature identified 24 previously reported COVID-19-associated MFS cases (including two children aged 7 and 11 years). Among these, anti-GQ1b positivity was variable, with many cases testing negative. The majority of cases had mild COVID-19, and some had no symptomatic infection. The paper notes that in a systematic review of 123 MFS patients, 85% were anti-GQ1b positive, but in COVID-19-associated MFS, negativity is more common.
**Clinical Implications:** This case highlights that MFS can occur after mild COVID-19, even in young children. The absence of anti-GQ1b antibodies does not rule out MFS, especially in COVID-19-associated cases. CSF albuminocytologic dissociation and electrophysiological findings (reduced SNAP amplitudes, absent H-reflexes) may have higher diagnostic value in this context. Spontaneous recovery is common, and immunotherapy may not be necessary unless overlapping GBS or Bickerstaff brainstem encephalitis is present. Clinicians should be aware that neurological complications of COVID-19 can occur early or after a delay, and periodic follow-up is recommended. The paper also notes that MFS can be triggered by COVID-19 vaccines, though this patient was unvaccinated.