A 28-year-old woman with a history of syphilis presents with a complaint of blurred vision and difficulty reading. On examination, she has a small, irregular pupil that reacts briskly to accommodation but shows no reaction to light (light-near dissociation). Both pupils show this finding. What is the drug of choice for preventing further progression of this condition?

## Argyll Robertson Pupil in Neurosyphilis: Pharmacological Management ### Clinical Diagnosis: Argyll Robertson Pupil (ARP) **Key Point:** The Argyll Robertson pupil is a pathognomonic sign of neurosyphilis (specifically tertiary syphilis affecting the dorsal midbrain). It is characterized by: - **Small, irregular pupils** - **Light-near dissociation** — no reaction to light but brisk reaction to accommodation - **Bilateral presentation** (usually) ### Pathophysiology The lesion involves the pretectal nucleus and dorsal midbrain in tertiary syphilis (neurosyphilis), damaging the afferent limb of the light reflex pathway while sparing the accommodation pathway. The irregular shape results from chronic inflammation and iris atrophy. ### Drug of Choice: Penicillin G (Intravenous) **High-Yield:** The Argyll Robertson pupil itself is NOT reversible once established, but penicillin G is the drug of choice because it is the first-line treatment for neurosyphilis and prevents further progression of the disease and additional neurological complications. ### Treatment Regimen for Neurosyphilis **Standard therapy:** - **Penicillin G (aqueous crystalline):** 18–24 million units/day IV in divided doses (3–4 million units every 4 hours) for 10–14 days - **Alternative (if penicillin allergy):** Ceftriaxone 2 g IV every 12 hours for 10–14 days **Rationale:** 1. Penicillin achieves high CSF concentrations and effectively eradicates *Treponema pallidum* 2. Prevents progression of neurosyphilis and development of general paresis of the insane (GPI) 3. Halts further pupillary dysfunction and other neurological sequelae 4. Standard of care per CDC and WHO guidelines ### Clinical Pearl **Reversibility:** The Argyll Robertson pupil is largely irreversible once established because the structural damage to the dorsal midbrain is chronic and fibrotic. However, penicillin prevents worsening and protects against other manifestations of tertiary syphilis (tabes dorsalis, GPI, cardiovascular syphilis). ### Mnemonic for Neurosyphilis Manifestations **"STING" (Tertiary Syphilis):** - **S** — Stroke (cerebrovascular) - **T** — Tabes dorsalis (dorsal column degeneration) - **I** — Iritis / **Argyll Robertson pupil** (ocular) - **N** — Neurosyphilis (general paresis of the insane, GPI) - **G** — Gumma (granulomatous lesions) ### Why Other Options Are Wrong | Drug | Why Not Used | | --- | --- | | **Pilocarpine** | Causes miosis but does NOT treat the underlying syphilis; it is a symptomatic measure only and does not prevent disease progression. | | **Atropine** | Causes mydriasis and would worsen visual symptoms; does not treat syphilis. | | **Timolol** | A β-blocker used for glaucoma; has no role in neurosyphilis management. | **Warning:** Symptomatic pupil-dilating or pupil-constricting agents do NOT address the underlying treponemic infection. Only antimicrobial therapy (penicillin) can halt disease progression.