What could be causing the patient's vision loss and lack of response to Ocrevus (ocrelizumab)?

Vision Loss with Lack of Response to Ocrelizumab: Differential Diagnosis and Workup

The most critical step is to obtain MRI orbits without and with IV contrast to evaluate for optic nerve pathology, followed by MRI brain without and with IV contrast to assess for demyelinating disease activity, alternative diagnoses, and serious complications of ocrelizumab including progressive multifocal leukoencephalopathy (PML). 1, 2

Primary Diagnostic Considerations

1. Alternative Demyelinating Disorders Misdiagnosed as MS

The lack of response to ocrelizumab should raise suspicion for antibody-mediated disorders that may have been initially misdiagnosed as MS:

• Neuromyelitis Optica (NMO): Shows bilateral simultaneous optic nerve enhancement with longer segment involvement, preferentially affecting posterior optic nerves, chiasm, or tracts 1
• MOG Antibody Disease (MOGAD): Demonstrates bilateral optic nerve involvement with characteristic optic nerve sheath and perioptic enhancement, typically affecting anterior optic nerve 1
• Chronic Relapsing Inflammatory Optic Neuropathy (CRION): Steroid-dependent recurrent optic neuritis 1

Key imaging distinction: MS characteristically shows shorter segment unilateral optic nerve involvement, while NMO and MOGAD show bilateral, longer segment disease 1. Obtain serum aquaporin-4 and MOG antibodies if not previously tested.

2. Progressive Multifocal Leukoencephalopathy (PML)

This is a life-threatening complication that has been reported with ocrelizumab in the postmarketing setting 2. PML presents with progressive neurologic deterioration including:

• Vision problems (progressive over days to weeks)
• Cognitive decline
• Motor weakness
• Balance problems

Critical point: PML has occurred in ocrelizumab-treated patients who had NO prior natalizumab exposure and were not on other immunosuppressants 2. If PML is suspected, immediately discontinue ocrelizumab and obtain urgent MRI brain with contrast plus JC virus PCR testing of CSF.

3. Microcystic Macular Edema (MMO)

A recent case report 3 documented progressive visual decline in an ocrelizumab-treated MS patient despite clinical and MRI stability. The patient developed MMO detected on optical coherence tomography (OCT) at 6 months, which progressively worsened over 5 years with:

• Gradual visual deterioration (from 0.7 to 0.3)
• Retinal neuroaxonal thinning
• No MS relapses or MRI activity

Action: Obtain OCT to evaluate for MMO, which represents ongoing neuroaxonal damage independent of inflammatory activity.

4. Ocrelizumab "Wearing-Off" Phenomenon

Recent evidence 4 shows that 57.6% of ocrelizumab-treated patients experience wearing-off symptoms, associated with:

• Higher plasma neurofilament light chain (indicating ongoing neuroaxonal damage)
• Reduced immunomodulation (elevated T lymphocytes)
• Symptoms starting 1-4 weeks before next infusion in many cases

Consider: If vision loss worsens cyclically before infusions, this may represent inadequate B-cell depletion. Check CD19+ B-cell counts and consider shortening infusion intervals.

5. Serious Herpes Virus Infections

The FDA label 2 warns that serious herpes infections (HSV, VZV) can affect the CNS, eyes, and disseminated sites in ocrelizumab-treated patients:

• Encephalitis and meningitis
• Intraocular infections (can cause vision loss)
• May be life-threatening

Examine for: Retinal necrosis, vitritis, or other signs of herpetic eye disease. If suspected, discontinue ocrelizumab until infection resolves.

6. Ischemic Optic Neuropathy

Consider anterior ischemic optic neuropathy (AION) or posterior ischemic optic neuropathy (PION), particularly if the patient has vascular risk factors 1. AION presents with:

• Optic disc edema
• Altitudinal visual field defects
• Acute onset

If ischemic optic neuropathy is suspected, subsequent vascular imaging (CTA or MRA head and neck) may be indicated 1.

7. Optic Nerve Neoplasm

Chronic progressive vision loss may indicate:

• Optic nerve glioma: More likely malignant in adults 1
• Optic nerve sheath meningioma: Classic presentation of chronic painless progressive vision loss 1

MRI orbits with contrast will characterize these lesions and their relationship to the optic nerve 5.

Recommended Diagnostic Algorithm

1. Immediate imaging:

   • MRI orbits without and with IV contrast (first-line for optic nerve pathology) 1
   • MRI brain without and with IV contrast (evaluate for PML, demyelinating lesions, intracranial extension) 1

2. Ophthalmologic evaluation:

   • OCT to detect MMO and measure retinal nerve fiber layer thickness 3
   • Fundoscopic examination for disc edema, pallor, vascular occlusions
   • Visual field testing

3. Laboratory testing:

   • Serum aquaporin-4 and MOG antibodies (if not previously done)
   • Plasma neurofilament light chain (marker of neuroaxonal damage) 4
   • CD19+ B-cell count (assess adequacy of B-cell depletion)
   • Consider lumbar puncture with JC virus PCR if PML suspected 2

4. Infection workup if clinically indicated:

   • HSV/VZV serology and PCR
   • Ophthalmologic examination for herpetic eye disease 2

Critical Safety Considerations

Do not continue ocrelizumab if:

• PML is suspected (discontinue immediately) 2
• Active serious herpes infection is present (withhold until resolved) 2
• Active HBV infection is confirmed 2

Common pitfall: Assuming all vision loss in MS patients on ocrelizumab represents MS disease activity. The evidence shows multiple alternative etiologies including drug-related complications (PML, infections), progressive neuroaxonal damage despite inflammatory control (MMO), and misdiagnosis of alternative demyelinating disorders 1, 2, 3.