Primary CNS Lymphoma: Causes, Symptoms, Diagnosis, and Treatment — Overview, Diagnosis & Treatment Options | MyMedicPlus

Primary central nervous system lymphoma (PCNSL) is an aggressive extranodal non-Hodgkin lymphoma confined to the brain, spinal cord, eyes, or leptomeninges without systemic involvement at diagnosis. It accounts for approximately 3–5% of all primary brain tumors and 4–6% of all extranodal lymphomas. The overwhelming majority (>90%) are diffuse large B-cell lymphoma (DLBCL) histologically, displaying activated B-cell (ABC) molecular subtype with characteristic MYD88 and CD79B mutations. PCNSL predominantly affects immunocompetent adults with a median age at diagnosis of 60–65 years, with a rising incidence attributable to an aging population. In immunocompromised patients — particularly those with HIV/AIDS or post-transplant iatrogenic immunosuppression — PCNSL is strongly associated with Epstein-Barr virus (EBV) reactivation and occurs at a younger age. Unlike systemic DLBCL, PCNSL is exquisitely sensitive to high-dose methotrexate but remains challenging to cure, with frequent relapses.

The cell of origin of PCNSL is a germinal center or post-germinal center B cell that has homed to the CNS sanctuary site. The exact mechanism by which lymphoma cells enter and proliferate within the CNS parenchyma — crossing the blood-brain barrier — remains incompletely understood but involves CXCL12-CXCR4 and CCL19-CCR7 chemokine axes enabling lymphocyte CNS trafficking. The most critical risk factor is immunosuppression: HIV infection (particularly CD4 counts below 50 cells/μL), solid organ transplantation with calcineurin inhibitors, primary immunodeficiency syndromes (Wiskott-Aldrich syndrome, CVID), and other forms of iatrogenic immunosuppression. In these settings, EBV-driven lymphoproliferation is the primary mechanism. In immunocompetent patients, the pathogenesis is less clear; recurrent somatic mutations in MYD88 L265P (~75% of cases) and CD79B (~30%) that activate the NF-κB pathway are characteristic and potential therapeutic targets. Age over 60, male sex, and possibly prior autoimmune disease modestly increase risk.

PCNSL most commonly presents with subacute neurological deficits developing over days to weeks. Focal deficits — hemiparesis, aphasia, ataxia, hemisensory loss — reflect mass effect from deep hemispheric lesions (basal ganglia, periventricular white matter, corpus callosum are classic sites). Cognitive changes and personality or behavioral change (frontal lobe involvement) are common and may be mistaken for dementia. Raised intracranial pressure causes headache, nausea, vomiting, and papilledema. Ocular involvement occurs in 15–25% of cases, presenting with blurred vision, floaters, or visual field defects from uveal/vitreous infiltration. Leptomeningeal disease causes meningismus, cranial nerve palsies, and radiculopathy. Constitutional B-symptoms (fever, night sweats, weight loss) are less prominent than in systemic lymphoma. Seizures occur in approximately 10–15% of cases. Spinal cord involvement causes myelopathy. The typical clinical course is progression over 4–6 weeks without treatment.

MRI brain with gadolinium contrast is the primary diagnostic tool. Classic PCNSL appears as one or more homogeneously enhancing, periventricular deep-white-matter lesions that may contact the ventricular surface. Lesions cross the corpus callosum ('butterfly glioma'-like pattern) and are associated with restricted diffusion on DWI (high DWI, low ADC) reflecting high cellularity. Leptomeningeal enhancement and vitreous enhancement may be present. Stereotactic brain biopsy is required for histopathological confirmation — corticosteroids should be withheld before biopsy if possible, as they cause lymphoma lysis and may produce false-negative results. CSF analysis by lumbar puncture (cytology, flow cytometry, cell-free DNA for MYD88 mutation) establishes leptomeningeal involvement in up to 40% of cases. Slit-lamp ocular examination detects uveal/vitreous infiltration. Testicular ultrasound is performed in males to exclude occult testicular lymphoma mimicking primary testicular DLBCL with CNS dissemination. HIV serology and EBV PCR are performed in all new diagnoses. Systemic staging with PET-CT confirms no systemic disease.

PCNSL is highly chemosensitive, and high-dose methotrexate (HD-MTX) is the cornerstone of treatment, achieving CNS penetration by overwhelming active transport mechanisms. Induction therapy for immunocompetent patients follows MATRix protocol (methotrexate 3.5 g/m² + cytarabine 2 g/m² × 2 days + thiotepa 30 mg/m² + rituximab 375 mg/m²) per the IELSG32 randomized trial, or MRI-PC regimen (rituximab, methotrexate 8 g/m², procarbazine, vincristine). Rituximab (anti-CD20) is incorporated into all B-cell PCNSL regimens. Consolidation strategies after induction include autologous stem cell transplantation (ASCT) with thiotepa-carmustine-busulfan conditioning for younger fit patients (preferred over whole-brain radiotherapy due to superior cognitive outcomes), or whole-brain radiotherapy (WBRT) at 23.4 Gy for patients not suitable for ASCT. Relapsed/refractory disease is treated with ibrutinib (BTK inhibitor targeting MYD88/CD79B pathway), lenalidomide, or HD-MTX re-challenge. Intrathecal chemotherapy is used for leptomeningeal disease. Ocular involvement is treated with intraocular methotrexate or combined systemic/local therapy. Patients with HIV-related PCNSL require antiretroviral therapy and less intensive chemotherapy due to immunosuppression.

The prognosis of primary CNS lymphoma (PCNSL) remains guarded despite advances in treatment. In immunocompetent adults treated with modern HD-MTX-based induction followed by autologous stem cell transplantation (ASCT) consolidation, 5-year progression-free survival ranges from 40–50% in selected younger patients who achieve complete remission. Elderly patients — over 70 years of age — who cannot tolerate intensive regimens have substantially worse outcomes, with 2-year overall survival of approximately 30–40%. Complete radiological response to HD-MTX induction is the single strongest prognostic factor, with patients achieving complete remission having significantly superior long-term outcomes compared to those with partial or no response. The IELSG prognostic scoring system (incorporating age, performance status, LDH, CSF protein, and deep brain involvement) effectively stratifies patients into risk groups. Whole-brain radiotherapy (WBRT), while effective for disease control, causes significant delayed neurotoxicity — particularly leukoencephalopathy and progressive cognitive decline — especially in patients over 60, which has driven preference for ASCT consolidation in eligible patients. Relapsed PCNSL carries a poor prognosis, with median overall survival of only 1–2 years after relapse despite salvage therapies including ibrutinib and ibrutinib-based combinations. HIV-related PCNSL outcomes have improved markedly with effective antiretroviral therapy and CD4 recovery. Long-term survivors face significant neurocognitive challenges from treatment effects, requiring ongoing neuropsychological monitoring and rehabilitation.

Prevention of PCNSL in immunocompetent patients is not possible given the poorly understood sporadic etiology. In HIV-infected patients, effective antiretroviral therapy to maintain CD4 counts above 200 cells/μL substantially reduces the risk of EBV-driven PCNSL; this is the most impactful preventive strategy in a high-risk group. In transplant recipients, judicious minimization of immunosuppression may reduce lymphoproliferative risk. Post-treatment surveillance requires serial brain MRI every 3 months for the first 2 years, then every 6 months up to 5 years, followed by annual imaging or sooner if symptoms recur. Neuropsychological assessment is important during surveillance as cognitive toxicity from WBRT and HD-MTX can be significant. Slit-lamp ophthalmological examination is repeated at each follow-up visit for patients with initial ocular disease. CSF analysis is repeated if leptomeningeal disease was present at diagnosis.

Any patient with subacute onset of focal neurological deficits — weakness on one side, speech difficulty, visual changes, ataxia — combined with cognitive change or behavioral alteration requires urgent neuroimaging. Patients with HIV infection developing new neurological symptoms — particularly headache, personality change, or focal signs — need emergency evaluation for PCNSL, CNS toxoplasmosis, or PML, which may require brain biopsy to distinguish. Recurrent visual floaters, blurred vision, or vitreous opacity in a middle-aged or older adult, particularly with no other ophthalmological explanation, should prompt a retinal and vitreal examination to exclude ocular PCNSL. Prior to brain biopsy in any patient with a ring-enhancing or homogenously enhancing CNS lesion, corticosteroids should ideally be withheld or minimized to avoid obscuring the diagnosis. A neuro-oncology team at a center experienced in PCNSL management should guide all treatment decisions given the complexity and rarity of this disease.