**Question:** All of the following are the features of Horner's syndrome Except -

A. Ptosis (drooping of the upper eyelid)
B. Miosis (narrowing of the pupil)
C. Anhidrosis (inability to sweat)
D. Paralysis of the eyebrow

**Core Concept:**
Horner's syndrome is a condition characterized by a decreased sensitivity to pain and temperature in the affected region due to damage to the sympathetic nervous system. The syndrome is typically caused by lesions involving the cervical sympathetic chain, such as those from a tumor, stroke, or injury. The primary features of Horner's syndrome are:

1. Ptosis: drooping of the upper eyelid due to denervation of the levator palpebrae muscle
2. Miosis: constriction of the pupil resulting from denervation of the pupillary constrictor muscle
3. Anhidrosis: reduced or absent sweating due to denervation of the eccrine sweat glands

**Why the Correct Answer is Right:**
The correct answer (D) refers to the paralysis of the eyebrow, which is not a primary feature of Horner's syndrome. In contrast, the other options are directly related to the sympathetic denervation in Horner's syndrome:

1. Ptosis (A) and Miosis (B) are directly related to the denervation of the levator palpebrae muscle and the pupillary constrictor muscle, respectively.
2. Anhidrosis (C) is caused by denervation of the eccrine sweat glands.
3. Paralysis of the eyebrow (D) is not a primary feature of Horner's syndrome; the primary features are ptosis, miosis, and anhidrosis.

**Why Each Wrong Option is Incorrect:**
Option A (paralysis of the eyebrow) is incorrect because it is not a primary feature of Horner's syndrome. The primary features focus on the effects of sympathetic denervation in the affected region.

Option B (paralysis of the eyelid) is incorrect as it is not a primary feature of Horner's syndrome. The primary features are ptosis (A) and miosis (B), which are directly related to sympathetic denervation.

Option C (paralysis of the eyelid) is incorrect as it is not a primary feature of Horner's syndrome. The primary features are ptosis (A) and miosis (B), which are directly related to sympathetic denervation.

**Clinical Pearl:**
Understanding the primary features of Horner's syndrome is crucial for accurate diagnosis as they represent the direct effects of sympathetic denervation. A thorough physical examination should focus on these features to identify Horner's syndrome.