Brainstem or cerebellar lesion: Vertical nystagmus is often associated with lesions in the brainstem or cerebellum, which can affect the vestibular pathways and cause this type of nystagmus. This is due to the critical role these areas play in the integration of sensory information for balance and eye movement.

Multiple sclerosis: This condition can cause lesions in the brainstem or cerebellum, leading to vertical nystagmus. The unpredictable nature of multiple sclerosis and its potential to affect various parts of the central nervous system make it a plausible diagnosis.
Stroke or vascular event: A stroke affecting the brainstem or cerebellum could result in vertical nystagmus. Given the high prevalence of stroke and its potential for causing a wide range of neurological deficits, it is a significant consideration.
Wernicke's encephalopathy: This condition, often related to thiamine deficiency, can cause nystagmus, including vertical nystagmus, among other neurological symptoms. Its association with alcohol misuse and malnutrition makes it a diagnosis to consider in certain patient populations.

Brain tumor: Although less common, a tumor in the brainstem or cerebellum could cause vertical nystagmus. Missing this diagnosis could have severe consequences, including delayed treatment and poor outcomes.
Central vertigo due to vertebral artery dissection: This condition can mimic inner ear vertigo but is due to a vascular issue and may present with vertical nystagmus. It is critical to identify this condition promptly due to the risk of stroke.
Medication-induced nystagmus: Certain medications can cause nystagmus as a side effect. Identifying and potentially adjusting the medication regimen could resolve the symptoms.

Congenital nystagmus: While typically horizontal, some forms of congenital nystagmus can have a vertical component. This diagnosis would be considered in patients with a long-standing history of nystagmus.
Paraneoplastic syndromes: Rarely, vertical nystagmus can be a presenting symptom of a paraneoplastic syndrome associated with certain cancers. This diagnosis requires a high index of suspicion and thorough investigation.
Infections affecting the central nervous system: Certain infections, such as abscesses or encephalitis, can cause vertical nystagmus. These conditions are rare but potentially life-threatening, necessitating prompt diagnosis and treatment.