Differential Diagnosis for Subacute Onset of Gait Imbalance

The patient's presentation of subacute onset of gait imbalance, ataxia on tandem walking, and a history of chronic smoking suggests a range of potential diagnoses. These can be categorized as follows:

• Single Most Likely Diagnosis
  • Cerebellar Degeneration or Atrophy: This condition often presents with subacute or chronic onset of ataxia, which affects gait and balance. The patient's symptoms of gait imbalance and ataxia on tandem walking are consistent with cerebellar dysfunction. Chronic smoking may contribute to vascular risk factors, potentially exacerbating cerebellar degeneration.
• Other Likely Diagnoses
  • Vitamin B12 Deficiency: This condition can cause subacute combined degeneration of the spinal cord, leading to ataxia, gait disturbances, and other neurological symptoms. Chronic smokers may have poor dietary habits, increasing the risk of vitamin deficiencies.
  • Alcohol-Related Cerebellar Ataxia: Although not explicitly mentioned, alcohol use is a common cause of cerebellar ataxia. Chronic smoking often correlates with alcohol consumption, making this a plausible consideration.
  • Spinocerebellar Ataxias (SCAs): These are a group of autosomal dominant genetic disorders that cause progressive ataxia. The subacute onset in this patient could be an initial presentation of an SCA.
• Do Not Miss Diagnoses
  • Multiple Sclerosis (MS): Although less common in presentation with isolated ataxia, MS can cause a wide range of neurological symptoms, including gait imbalance. It's crucial to consider MS due to its potential for significant morbidity if left untreated.
  • Structural Lesions (e.g., Cerebellar Tumors, Stroke): These can present with ataxia and gait disturbances. Given the potential for serious outcomes, including death or significant disability, it's critical to rule out such lesions.
  • Infectious or Inflammatory Causes (e.g., Cerebellitis, Abscess): These conditions require prompt diagnosis and treatment to prevent serious complications or death.
• Rare Diagnoses
  • Paraneoplastic Cerebellar Degeneration (PCD): This is a rare condition associated with certain cancers, where the immune system mistakenly attacks the cerebellum, leading to ataxia. Given the patient's smoking history, which increases cancer risk, PCD is a rare but important consideration.
  • Toxic or Metabolic Causes (e.g., Mercury Poisoning, Hypothyroidism): These can cause ataxia and gait disturbances. While rare, they are important to consider due to their potential reversibility with appropriate treatment.

Investigations Needed

• Imaging: MRI of the brain, particularly focusing on the cerebellum, to rule out structural lesions, degeneration, or inflammation.
• Laboratory Tests: Complete blood count (CBC), electrolyte panel, liver function tests, vitamin B12 level, and thyroid function tests to identify metabolic or toxic causes.
• Genetic Testing: Consideration for spinocerebellar ataxia panel if familial history suggests or if initial evaluations are inconclusive.
• Lumbar Puncture: May be necessary if multiple sclerosis, infectious, or inflammatory causes are suspected.
• Toxicology Screen: Depending on the clinical context, to rule out substance-induced ataxia.