Prolonged isolated dysgeusia as an initial manifestation of neurolymphomatosis in primary central nervous system lymphoma: illustrative case.

backgroundNeurolymphomatosis (NL) is an uncommon manifestation of lymphoma caused by direct nerve infiltration and often presents with nonspecific neurological symptoms, leading to delayed diagnosis. Isolated cranial nerve symptoms as an initial presentation are rare and may be overlooked. OBSERVATIONS: An 85-year-old woman presented with dysgeusia persisting for approximately 12 months, followed 2 months later by the development of diplopia, left peripheral facial nerve palsy, and left facial sensory disturbance. Contrast-enhanced MRI demonstrated enlargement and enhancement of the left trigeminal nerve, as well as enhancement of the facial and vestibulocochlear nerves within the internal auditory canal, along with an enhancing parenchymal lesion in the left frontal lobe. Biopsy of the frontal lobe lesion revealed diffuse large B-cell lymphoma, and bone marrow examination showed no systemic involvement, leading to the diagnosis of primary central nervous system lymphoma (PCNSL) with concurrent NL. Chemotherapy resulted in marked clinical improvement and resolution of imaging abnormalities. LESSONS: Isolated and subtle cranial nerve symptoms, such as dysgeusia, may precede overt neurological deficits in NL associated with PCNSL. Contrast-enhanced MRI should be considered early when the diagnosis remains unclear, as noncontrast imaging may fail to detect early cranial nerve involvement. https://thejns.org/doi/10.3171/CASE26296.