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Updated: May 16, 2026

A Primary Neuron Culture System for the Study of Herpes Simplex Virus Latency and Reactivation
Published on: April 2, 2012
The floccular syndrome in herpes simplex type 1 encephalitis
Aasef G Shaikh1, Pichet Termsarasab, David E Riley
1Department of Neurology, Case Western Reserve University, Cleveland, OH, United States. aasefshaikh@gmail.com
Herpes simplex virus type 1 (HSV1) encephalitis can cause downbeat nystagmus, potentially linked to flocculus damage. Treatment with acyclovir improved both the encephalopathy and the nystagmus.
Area of Science:
- Neurology
- Infectious Diseases
- Ophthalmology
Background:
- Herpes simplex virus type 1 (HSV1) is a common cause of sporadic fatal encephalitis.
- Ocular motor disturbances, such as nystagmus, can occur in patients with HSV1 encephalitis.
Observation:
- A patient with HSV1 encephalitis presented with downbeat nystagmus, more pronounced in primary gaze and attenuated in upgaze.
- Brain MRI revealed characteristic HSV1 lesions and additional hyperintensities in the bilateral flocculi.
Findings:
- Cerebrospinal fluid analysis confirmed HSV1 infection.
- The observed downbeat nystagmus pattern suggested involvement of the flocculus, a key cerebellar structure for gaze stabilization.
Implications:
- This case highlights the flocculus as a potential target of HSV1 in encephalitis.
- Successful treatment with acyclovir suggests that antiviral therapy can resolve both neurological deficits and associated ocular motor abnormalities.
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