A 19 year old young girl with previous history of repeated pain over medial canthus and chronic use of nasal decongestants, presented with abrupt onset of fever with chills & rigor, diplopia on lateral gaze, moderate proptosis & chemosis. On examination optic disc is congested. Most likely diagnosis is –
**Core Concept:** **Optic neuritis** is an inflammation of the optic nerve, which can lead to visual disturbances. Optic neuritis can be primary (idiopathic) or secondary to another underlying condition like demyelinating disorders, infections, or autoimmune diseases.
**Why the Correct Answer is Right:** In this case, the patient presents with abrupt onset of fever, chills, rigors, diplopia, proptosis, and chemosis, along with congested optic disc on examination. Given the patient's history of chronic nasal decongestant use, it is more likely that the optic neuritis is secondary to an autoimmune process, specifically neuromyelitis optica (NMO). Optic neuritis in NMO is typically bilateral, and it is associated with aquaporin-4 autoantibodies (AQP4-Abs), which are not typically present in multiple sclerosis (MS).
**Why Each Wrong Option is Incorrect:**
A. **Multiple Sclerosis (MS)** is a demyelinating disorder affecting the central nervous system. While optic neuritis is a common symptom in MS, the abrupt onset of fever, chills, rigors, diplopia, proptosis, and chemosis are more consistent with NMO.
B. **Viral infections** can cause optic neuritis, and fever is a common symptom. However, the abrupt onset of fever, chills, and rigors, along with the patient's history of chronic nasal decongestant use, suggest a more specific diagnosis of NMO.
C. **Autoimmune disorders** like rheumatoid arthritis and systemic lupus erythematosus can cause optic neuritis. However, the abrupt onset of symptoms and the history of chronic nasal decongestant use support a diagnosis of NMO over these conditions.
D. **Neurotoxic agents** like decongestants are not typically associated with optic neuritis. The abrupt onset of symptoms and the history of chronic nasal decongestant use point towards an autoimmune disorder like NMO.
**Clinical Pearl:** Optic neuritis is a clinical manifestation of the autoimmune disorder neuromyelitis optica (NMO) associated with aquaporin-4 antibodies (AQP4-Abs). The abrupt onset of symptoms, fever, and history of chronic decongestant use should prompt clinicians to consider NMO, which is distinct from multiple sclerosis (MS), which presents with a more chronic course and relapsing-remitting pattern of disease progression.