Differential Diagnosis for Horizontal Nystagmus and Associated Symptoms

The patient's presentation of horizontal nystagmus in the right eye, impaired smooth pursuit to the right, increased dizziness with horizontal saccades, and decreased convergence of the right eye suggests a complex oculomotor and vestibular dysfunction. The differential diagnoses can be categorized as follows:

• Single Most Likely Diagnosis
  • Lateral Medullary Syndrome (Wallenberg's Syndrome): This condition, caused by a stroke in the lateral medulla, can lead to a combination of symptoms including nystagmus, impaired smooth pursuit, and vestibular dysfunction. The decreased convergence could be related to the involvement of the medial longitudinal fasciculus (MLF) or other nearby structures affecting oculomotor functions.
• Other Likely Diagnoses
  • Vestibular Neuritis: Inflammation of the vestibular nerve can cause severe vertigo, nystagmus, and imbalance. While it primarily affects the vestibular system, it could indirectly affect oculomotor functions, including smooth pursuit and convergence.
  • Benign Paroxysmal Positional Vertigo (BPPV): Although BPPV typically presents with vertigo triggered by specific head movements, some patients may experience nystagmus and impaired vestibular function that could contribute to the patient's symptoms.
  • Cerebellopontine Angle (CPA) Tumors: Tumors in this region, such as acoustic neuromas, can compress the vestibulocochlear nerve and adjacent structures, leading to a variety of symptoms including nystagmus, vestibular dysfunction, and impaired oculomotor functions.
• Do Not Miss Diagnoses
  • Posterior Circulation Stroke: Strokes in the posterior circulation can present with a wide range of symptoms including sudden onset vertigo, nystagmus, and oculomotor disturbances. Early recognition is crucial for timely intervention.
  • Multiple Sclerosis (MS): MS can cause a variety of neurological symptoms, including oculomotor disturbances and vestibular dysfunction. The disease's unpredictable course and potential for significant disability make it a critical diagnosis not to miss.
  • Wernicke's Encephalopathy: This condition, caused by thiamine deficiency, can lead to oculomotor abnormalities, including nystagmus, and vestibular symptoms. It is a medical emergency requiring prompt treatment.
• Rare Diagnoses
  • Spinocerebellar Ataxia (SCA): A group of autosomal dominant disorders that can affect the cerebellum and lead to ataxia, oculomotor disturbances, and vestibular dysfunction.
  • Chiari Malformation: A structural defect in the cerebellum that can cause a range of neurological symptoms, including vestibular and oculomotor disturbances, due to compression of the brainstem and cerebellum.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, imaging studies (such as MRI), and sometimes additional tests (like electronystagmography or caloric testing) to determine the underlying cause of the symptoms.