**Question:** Bilateral ptosis is not seen in

A. Myasthenia gravis
B. Horner's syndrome
C. Paralysis due to facial nerve palsy
D. Ptosis due to thyroid eye disease

**Core Concept:** Ptosis refers to the involuntary drooping of the upper eyelids, which can be caused by various medical conditions or medications. These conditions may affect the motor nerves, neuromuscular junctions, or the muscles themselves.

**Why the Correct Answer is Right:** Bilateral ptosis is a rare clinical presentation, and understanding the underlying causes can help differentiate between different medical conditions. In this case, the correct answer (B) is related to Horner's syndrome, which is characterized by a combination of symptoms, including ptosis, miosis (constriction of the pupil), enophthalmos (eye sinking), and decreased sweating. Horner's syndrome is typically caused by damage to the sympathetic trunk or its branches, leading to a decrease in sympathetic innervation to the affected eye.

**Why Each Wrong Option is Incorrect:**

A. Myasthenia gravis is a neuromuscular disorder characterized by fatigable muscle weakness. Although ptosis is a common symptom in myasthenia gravis, it is not exclusively bilateral.

C. Facial nerve palsy (House-Brackmann Grade VI) typically results in unilateral ptosis, not bilateral ptosis.

D. Thyroid eye disease (or Graves' orbitopathy) often presents with ptosis, but it is typically unilateral, not bilateral.

**Clinical Pearl:** Bilateral ptosis should raise suspicion for Horner's syndrome, prompting further diagnostic evaluation for the underlying cause. Differentiating between unilateral and bilateral ptosis helps narrow down the differential diagnosis and guides appropriate investigations and management.

**Correct Answer:** B. Horner's syndrome