Tumor-induced central neurogenic hyperventilation (CNH) is exceedingly rare. CNH is defined by hyperventilation with low arterial PaCO₂, high arterial PaO₂, and high arterial pH without drug or metabolic causes [1,2]. Most cases of tumor-induced CNH result from primary CNS despite their rarity, comprising only 4% of primary CNS tumors [2,3]. Tumor-induced CNH resulted from CNS lymphoma in nearly 60% of tumor-induced CNH [2,4-15]. Most tumor-induced CNH results from infiltrating tumor in the pons or medulla, less commonly in the setting of diffuse cerebral disease [2,5]. The presumed mechanism is activation of respiratory centres and central chemoreceptors [2]. All previously reported cases presented with CNH at diagnosis. We present an immunocompetent woman with previously diagnosed PCNSL presenting with CNH at first recurrence. Tumor-induced CNH proved uniformly fatal in essentially all cases.

A 75 year-old, immunocompetent woman presented with months of progressive dementia and aphasia. A brain MRI revealed diffuse cerebral, predominantly subcortical, non-enhancing disease (Figure 1A). There was a single site of enhancement in the left caudate and negligible diffusion restriction noted (Figures 1B-1C). Stereotactic biopsy of single enhancing lesion revealed pathology consistent with diffuse large B cell lymphoma. Hematoxylin and Eosin (H&E) showed large atypical lymphoid cells in an angiocentric pattern and with scant cytoplasm, large pleomorphic nuclei with clumped chromatin, nuclear moulding and occasionally prominent nucleoli (Figure 2A). Scattered mitoses were seen. Immunohistochemistry was positive for CD20 (Figure 2B) and MUM1. Subsets were positive for BCL2 and BCL6 and few for CD10. Small mature CD3 T lymphocytes infiltrate was detected. The Ki67 proliferation index was as high as 80-90% (Figure 2C).

Figure 1: Brain imaging findings. Brain MRI findings were atypical for primary CNS lymphoma (PCNSL), defined by predominantly non enhancing disease on fluid attenuation inversion recovery (FLAIR) images (A,D,E,F,H) and no associated restricted diffusion was ever noted (C). FLAIR diseases was restricted to cerebral hemispheres at presentation (A), limited to periaqueductal grey brainstem at recurrence (E-F) and diffuse but predominantly supratentorial prior to death (H). The single faintly enhancing focus in left caudate (B) at presentation was targeted for biopsy. Remission was notable for residual FLAIR signal restricted to subcortical white matter and consistent with methotrexate-induced leukodystrophy (D). The recurrent disease in the brainstem presenting with central neurogenic hyperventilation was avid on fluorodeoxyglucose positron emission tomography (FDG-PET, G).

Figure 2: Pathology of brain biopsy. H&E shows large atypical lymphoid cells in an angiocentric pattern and with scant cytoplasm, large pleomorphic nuclei with clumped chromatin, nuclear molding, and occasionally prominent nucleoli (A, 4x). Scattered mitoses seen. Immunostaining: positive for CD20 (B, 4x), MUM1; subset positive for BCL2, BCL6; few positive for CD10. Small mature CD3 T lymphocytes infiltrate lesion. Ki67 index up to 80-90% (C, 4x).

Brain and body Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) revealed no systemic involvement, consistent with Primary CNS Lymphoma (PCNSL). Flow cytometry and cytology revealed no Cerebrospinal Fluid (CSF) dissemination. A bone marrow biopsy revealed mild B-cell lymphocytosis inconclusive for marrow involvement. She was treated with 5 cycles of biweekly intravenous rituximab (500 mg/m²) and methotrexate. Methotrexate was increased from 3.5 to 8.0 gm/m² while the initial procarbazine (100 mg/m²) and vincristine 2 mg was switched to monthly temozolomide (150 mg/m²) for a total of 2.5 months of therapy. After repeat brain MRI revealed remission (Figure 1D), she underwent consolidation therapy with cytarabine (3 gm/m² day 1-2, q3 weeks). Over the course of this therapy, she improved clinically with a dramatic improvement in her initial encephalopathy, once again living independently.

At 4 months from diagnosis and shortly after consolidation therapy, she developed intractable emesis without clear gastrointestinal cause and hyperventilation without cardiopulmonary etiology. Serial blood glasses marked revealed respiratory alkalosis (maximal pH=7.67, respiration=27, pO₂=241; minimum pCO₂=10). She remained otherwise neurologically intact. For suspicion of central neurogenic hyperventilation (CNH), she was intubated and brain MRI performed. While there was no clear supratentorial disease progression (Figure 1E), there was new non enhancing FLAIR disease extending from dorsal midbrain to the vermis (Figure 1F). Repeat brain FDG-PET revealed high glucose uptake associated with the new FLAIR disease in the pontine tegmentum (Figure 1G), consistent with recurrent PCNSL. CSF profile revealed normal protein (40 mg/dL), RBC 97/μL, WBC 3/μL (88% lymphocytes) with negative bacterial cultures, toxoplasma IgG and HSV, JC, CMV, EBV and JC PCRs. Flow cytometry and cytology again revealed no lymphoma cells.

To palliate and spare cognitive neurotoxicity, she was treated with involved field radiation to posterior fossa radiation (30Gy in 17 fractions), dexamethasone 40 mg/day, and off-label nivolumab 3 mg/kg q2 weeks with resolution of CNH. Disease remission was only brief. By 4 months after recurrent PCNSL presenting with CNH, brain MRI revealed diffuse non enhancing disease progression, including the brainstem but more pronounced in the cerebral hemispheres (Figure 1H). She was transferred to hospice and died shortly after 9 months after her initial diagnosis.

Central Neurogenic Hyperventilation (CNH) is exceedingly rare and portends poor prognosis in reported cases. Despite their rarity, comprising only 1% of all CNS tumors, CNS Lymphoma (CNSL) leads to 58% (15/26) of reported cases, mostly (13/15) Primary CNS Lymphoma (PCNSL) [2,4-15]. The remaining cases were comprised of 31% (8/26) gliomas [16-23], <4% (1/26) medulloblastoma [24], <4% (1/26) ganglioglioma [25] and <4% (1/26) invasive laryngeal carcinoma [26]. 77% (20/26) of tumor-induced CNH cases resulted from direct tumor infiltration into the pontine tegmentum and medulla, leading to activation of respiratory centres and central chemoreceptors [2]. The remaining cases had diffuse cerebral disease, mostly CNS lymphoma cases [2,5]. We present the first case of PCNSL presenting with CNH at recurrence. All prior cases of tumor-induced CNH presented at the time of diagnosis. CNH should raise suspicion of CNS lymphoma in undiagnosed patients and suggest recurrence in confirmed cases of CNS lymphoma. Antineoplastic therapy is vital for controlling PCNSL-induced CNH. Survival is uniformly dismal after presenting with tumor-induced CNH.

We present the first case of recurrent primary CNS lymphoma leading to Central Neurogenic Hyperventilation (CNH). CNH was a presenting symptom in all previously reported cases of CNS lymphoma, comprising nearly 60% of reported cases of tumor-induced CNH despite their rarity. Tumor-induced CNH raises the probability of CNS lymphoma in undiagnosed cases and of recurrence in diagnosed cases. Tumor-induced CNH predicts short-interval death in most cases.

• Primary CNS lymphoma comprises ~1% of all CNS tumors and ~2.3% of primary CNS tumors.

• Tumor-induced central neurogenic hyperventilation (CNH) is exceedingly rare and uniformly fatal.

• Tumor-induced CNH is caused by CNS lymphoma in nearly 60% of reported cases.

• CNH should raise suspicion of CNS lymphoma in undiagnosed patients and suggest recurrence in confirmed cases of CNS lymphoma.