Differential Diagnosis for Dizziness and Falling

The patient's symptoms of dizziness, falling due to legs "giving out," severe bilateral horizontal nystagmus, and left dysmetria on finger-nose-finger testing suggest a neurological cause. Here's a categorized differential diagnosis:

• Single Most Likely Diagnosis

  • Vestibular Neuritis or Labyrinthitis: The presence of severe bilateral horizontal nystagmus is highly suggestive of a vestibular system disorder. Vestibular neuritis or labyrinthitis could explain the dizziness and the physical examination findings, including nystagmus and dysmetria, due to the involvement of the vestibular system and its connections with the cerebellum.

• Other Likely Diagnoses

  • Cerebellar Stroke or Infarct: The left dysmetria and the symptom of legs "giving out" could indicate a cerebellar lesion. A stroke in the cerebellum could cause these symptoms, along with nystagmus, due to the cerebellum's role in coordination and balance.
  • Multiple Sclerosis (MS): MS could present with a wide range of neurological symptoms, including dizziness, ataxia (leading to falls), and nystagmus. The optic neuritis form of MS could also lead to similar symptoms if the brainstem or cerebellum is involved.
  • Benign Paroxysmal Positional Vertigo (BPPV): Although BPPV typically presents with vertigo triggered by specific head movements, some patients might experience persistent dizziness and imbalance, potentially leading to falls. However, the presence of dysmetria and severe nystagmus might be less typical for BPPV.

• Do Not Miss Diagnoses

  • Posterior Circulation Stroke: A stroke in the posterior circulation (including the vertebrobasilar system) can present with a variety of symptoms, including dizziness, ataxia, and visual disturbances. Given the potential for rapid progression and severe consequences, it's crucial not to miss this diagnosis.
  • Brainstem Tumor: A tumor in the brainstem could cause a combination of cranial nerve deficits, ataxia, and nystagmus. Although less common, this diagnosis is critical due to its implications for treatment and prognosis.
  • Wernicke's Encephalopathy: This condition, caused by thiamine deficiency, can present with ataxia, ophthalmoplegia, and confusion. It's a medical emergency that requires immediate treatment to prevent long-term neurological damage.

• Rare Diagnoses

  • Spinocerebellar Ataxia (SCA): This group of genetic disorders affects the cerebellum and can cause progressive ataxia, dysarthria, and nystagmus. While the onset is typically earlier in life, some forms can present later, making it a consideration in the differential diagnosis of ataxia and dizziness.
  • Acute Cerebellitis: Inflammation of the cerebellum can cause acute ataxia, dysmetria, and nystagmus. It's a rare condition but should be considered, especially in the context of recent infection or autoimmune disorders.