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Purpose: Waldenström macroglobulinemia (WM) is a rare non-Hodgkin lymphoma characterized by the presence of a monoclonal immunoglobulin M protein (M-protein). We report a case of WM with increasing M-protein levels and subsequent retinal vascular alterations consistent with hyperviscosity retinopathy, prompting quick escalation of hemato-oncological therapy.

Case presentation: A 55-year-old Caucasian woman presented to our clinic with a foreign body sensation in her left eye. Slit-lamp examination revealed a benign conjunctival inclusion cyst. Apart from mild arteriovenous nicking indicative of grade 2 hypertensive retinopathy, the anterior and posterior segments were otherwise unremarkable. During medical history, however, the patient reported a diagnosis of WM made in June 2024. We established a surveillance plan consisting of dilated pupil examinations and visual field testing (VFT) every four to six months. The patient’s general practitioner and hemato-oncologist were apprised. All involved physicians were advised to notify us in the event of rising M-protein levels. Six months after initial presentation, retinal findings remained virtually unchanged except for moderate improvement in arteriovenous nicking. 12 months after initial presentation, the treating hemato-oncologist informed us of progressive increases in M-protein levels reaching 32.30 g/L and the planned initiation of riuximab/bendamustin. We immediately scheduled the patient for further evaluation. Funduscopy revealed characteristic signs of early hyperviscosity syndrome including dilated and tortuous veins with a sausage-link appearance and intravascular sludging in both eyes. No blot or flame hemorrhages and no signs of venous occlusion or papilledema could be observed. For baseline documentation, ultra-widefield fundus photography and infrared optical coherence tomography of the macula were performed. Following the diagnosis of hyperviscosity syndrome, the oncological therapy was adjusted accordingly. During subsequent visits at intervals of two to three months, the previously observed venous alterations showed first signs of regression.

Conclusions: While hyperviscosity syndrome represents a rare complication of WM, the risk of its manifestation correlates with increasing M-protein levels. This report underscores the importance of regular ophthalmological monitoring with detailed fundus examination and VFT, with particular attention to the retinal vasculature. The emergence of new vascular abnormalities, including intravascular sludging and sausage-link venous engorgement as part of a hyperviscosity retinopathy warrants immediate referral back to oncology for further reassessment and adjustment of oncological therapy.