A 75 year old lady wakes up with sudden painless loss of vision. She gives history of scalp tenderness and cramp like pain on eating. O/E there is a pale disc edema, has an inferior altitudinal field defect. What is the likely cause?
**Core Concept:** Optic Neuritis, Papilledema, Optic Disc Edema, Field Defect, Disc pallor
**Why the Correct Answer is Right:**
The correct answer is **C.** Optic neuritis. The patient presents with sudden painless loss of vision, scalp tenderness, and cramp-like pain on eating, which are indicative of a central nervous system (CNS) disorder. The ocular examination reveals a pale disc edema, inferior altitudinal field defect, and optic disc pallor, which are characteristic findings of optic neuritis.
**Why Each Wrong Option is Incorrect:**
A. Migraine (A) is a vascular headache rather than a neurological disorder, which does not cause optic disc pallor, field defect, or optic neuritis.
B. Encephalitis (B) is an inflammation of the brain, typically caused by viral infections. Optic neuritis is a specific manifestation of encephalitis but does not cause optic disc pallor or inferior altitudinal field defect.
D. Multiple Sclerosis (D) is a demyelinating disease affecting the CNS, but optic neuritis is a common presenting symptom in MS patients. The other symptoms and examination findings in this case do not align with MS.
**Why Each Wrong Option is Incorrect:**
Encephalitis (option B) is a wrong answer because optic neuritis is a specific manifestation of encephalitis but does not cause optic disc pallor or inferior altitudinal field defect.
Migraine (option A) is incorrect because optic disc pallor and inferior altitudinal field defect are not typical findings in migraine.
Multiple Sclerosis (option D) is wrong because the patient does not present with typical MS symptoms like fatigue, bladder dysfunction, or bowel incontinence, nor does she have the characteristic MRI findings of MS plaques.
**Core Concept:** Optic Neuritis
**Why the Correct Answer is Right:**
The correct answer, optic neuritis, is an inflammation of the optic nerve, specifically the optic disc. Optic neuritis can cause visual disturbances like sudden loss of vision, disc pallor, and field defects. This condition is one of the presenting symptoms in multiple sclerosis (MS) patients. However, in this case, the patient's clinical features are more consistent with optic neuritis, which is a non-demyelinating disorder affecting the optic nerve.
**Why Other Options are Incorrect:**
Encephalitis (option B) is incorrect because optic neuritis is a specific manifestation of encephalitis, but this case does not involve the optic nerve, which is the primary focus of the question.
Migraine (option A) is incorrect because optic disc pallor and inferior altitudinal field defect are not typical findings in migraine. Migraine typically presents with visual disturbances like scotomata, photophobia, nausea, and vomiting, rather than the specific findings mentioned in the question.
Multiple Sclerosis (option D) is incorrect because while optic neuritis is a symptom in MS, the patient's clinical