Anhydrosis is more prominent in which type of Horner's syndrome?

• A. Pre-ganglionic
• B. Post-ganglionic
• C. Both equally
• D. Neither

Answer: (A)

Anhidrosis in Horner's syndrome depends on where the sympathetic pathway to the face is interrupted. The sudomotor (sweat) fibers travel from the spinal cord to the superior cervical ganglion and then continue to the facial sweat glands. If the lesion is preganglionic, occurring before the superior cervical ganglion, the signal to all postganglionic neurons that would drive facial sweating is cut off, so sweating is markedly reduced on the affected side. If the lesion is postganglionic, after the superior cervical ganglion, some sudomotor fibers may still reach the facial glands (via collateral routes), so sweating is less severely affected. Therefore anhidrosis tends to be more prominent in preganglionic Horner's syndrome—the interruption happens upstream of the ganglion, producing a greater loss of sweating.