Which condition is characterized by bilateral horizontal nystagmus and lacks acute febrile illness?

The condition characterized by bilateral horizontal nystagmus that occurs without an acute febrile illness is post-infectious cerebellitis. This condition is often a result of a viral infection that has led to an inflammatory response affecting the cerebellum. Unlike acute vestibular neuritis, which is usually associated with an acute viral illness and typically presents with unilateral symptoms, post-infectious cerebellitis can manifest as bilateral nystagmus due to its impact on cerebellar function.

In the case of meningitis, symptoms typically include a fever and signs of meningeal irritation, which are not present in post-infectious cerebellitis. Additionally, while vertigo can present with nystagmus, it is more of a symptom than a specific diagnosis and usually does not describe the specific characteristics associated with post-infectious cerebellitis. This differentiation highlights the importance of identifying the underlying cause and associated symptoms when diagnosing such conditions.