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Syphilitic Optic Neuritis

URGENT — Systemic

Symptoms

  • visual loss: acute or subacute, often sudden and severe; more commonly bilateral than MS-related ON
  • pain: retro-orbital or periocular discomfort, but typically less prominent than in demyelinating ON
  • dyschromatopsia: significant decrease in color vision perception
  • systemic signs: secondary syphilis may present with a rash (palms/soles), fever, and malaise
  • neurologic: headache or stiff neck may suggest concurrent syphilitic meningitis

Clinical Findings

Clinical presentation

  • disc edema (papillitis): often more pronounced than MS-ON, frequently with peripapillary hemorrhages
  • rapd: present in unilateral or asymmetric cases
  • intraocular inflammation: vitritis and anterior chamber cells are common (hallmark markers for infectious ON)

Posterior segment signs

  • asppc: large, yellowish, damp-looking placoid chorioretinal lesions in the macula
  • neuroretinitis: disc edema associated with a macular star (hard exudates)
  • retinal vasculitis: dilated, tortuous vessels and perivascular sheathing

Visual function

  • visual fields: central or cecocentral scotomas are typical

Etiology

Pathogen

  • treponema pallidum: spirochetal infection; "The Great Imitator"
  • stage: can occur at any stage, but ocular involvement most commonly reflects secondary or early tertiary syphilis
  • co-infection: HIV significantly increases the risk and aggressiveness of neurosyphilis/ocular syphilis

Red Flags

  • steroids alone: never treat presumed ON with steroids without ruling out syphilis; steroids without antibiotics worsen the infection
  • hiv status: mandatory testing for all ocular syphilis patients due to high co-infection rates
  • vitritis + swollen disc: this combination almost never happens in MS; strongly suspect syphilis or sarcoidosis
  • jarisch-herxheimer: systemic flu-like reaction within 24h of starting IV Penicillin

Investigations

Serology (the essential pair)

  • treponemal (confirmatory): FTA-ABS or TP-PA (once positive, usually positive for life)
  • non-treponemal (quantitative): RPR or VDRL (used to monitor disease activity and treatment response)

Neuro workup

  • lumbar puncture: mandatory; CSF VDRL, cell count, and protein to assess neurosyphilis
  • mri brain/orbits: look for optic nerve enhancement and leptomeningeal involvement

Ocular baseline

  • oct: to monitor the retinal nerve fiber layer (RNFL) and macula

Treatment

First-line antibiotics

  • aqueous penicillin g: 18–24 million units/day IV (continuous or q4h) for 10–14 days
  • penicillin allergy: Ceftriaxone 2g IV/IM daily; however, penicillin desensitization is preferred

Adjuvants

  • corticosteroids: may be added AFTER antibiotics are started to control inflammation, at expert discretion

Public health

  • infectious disease consult and mandatory reporting to local health authorities

Clinical Pearl

The great imitator. Syphilitic ON is frequently misdiagnosed as MS-related or AION. Steroids without penicillin worsen outcome. Test everyone.

Differential Diagnosis

  • • idiopathic optic neuritis (MS-associated; rarely has vitritis)
  • • nmosd (typically more severe visual loss, long spinal cord lesions)
  • • sarcoidosis (also causes vitritis and disc edema; check ACE/Chest CT)
  • • lyme disease (similar presentation; check Lyme titers)

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