USMLE Step 1 Review/Neurology

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Localization[edit]

Small, irregular pupil that does not react to light but does react to accommodation.

Localization is to the midbrain and the cause is neurosyphilis. The pupil's better response to a near than to a light stimulus is because the lesion involves the more dorsally-located fibers that subserve the pupil response to light and spares the more ventrally-located fibers that subserve the pupil response to accommodation.

Care should be taken to not confuse Argyll-Robertson pupil with an Adie's tonic pupil, Horner's syndrome or third nerve lesions.

Regarding what to do in case of syncope:[edit]

If the face is red, raise the head.

If the face is pale, raise the tail!