Differential Diagnosis

The patient's presentation suggests a complex condition with optic neuritis as a primary symptom. Given the information, here's a structured approach to the differential diagnosis:

• Single Most Likely Diagnosis

  • Multiple Sclerosis (MS): This is a leading consideration due to the presentation of optic neuritis, which is a common initial symptom of MS. The lack of response to treatments like corticosteroids (implied by "Comac sound or the other medication") and the absence of a clear alternative diagnosis support this possibility.

• Other Likely Diagnoses

  • Idiopathic Optic Neuritis: This condition can occur without a clear underlying cause and might not necessarily be the first presentation of MS. The normal investigations and lack of systemic symptoms make this a plausible option.
  • Neuromyelitis Optica Spectrum Disorder (NMOSD): Although less common than MS, NMOSD can present with optic neuritis and typically has a more severe course. The absence of a clear family history or systemic symptoms does not rule out this condition.

• Do Not Miss Diagnoses

  • Sarcoidosis: This systemic disease can cause optic neuritis among other symptoms. It's crucial to consider because it requires specific treatment and can have significant morbidity if missed.
  • Lyme Disease: Given the potential for optic neuritis as a manifestation, especially in endemic areas, Lyme disease should be considered, particularly if there's any history of tick exposure.
  • Vitamin Deficiency (other than B12): Although B12 and iron levels are normal, deficiencies in other vitamins or nutrients could potentially contribute to neurological symptoms.

• Rare Diagnoses

  • Leber's Hereditary Optic Neuropathy (LHON): A rare mitochondrial inherited disorder that leads to optic neuritis and vision loss, primarily in young males but can occur in females.
  • Chronic Relapsing Inflammatory Optic Neuropathy (CRION): A rare condition characterized by recurrent episodes of optic neuritis without a clear systemic cause.
  • Optic Neuritis due to other Infections (e.g., Tuberculosis, Syphilis): Although syphilis was mentioned as negative, it's essential to ensure all infectious causes are thoroughly ruled out, especially in cases where the diagnosis remains elusive.

Each of these diagnoses requires careful consideration of the patient's history, physical examination, and additional diagnostic tests to determine the most appropriate diagnosis and treatment plan.