A Rare Case of Hypoglossal Nerve Neurolymphomatosis in a Patient Treated With Diffuse Large B‐Cell Lymphoma

A 59-year-old man who was initially investigated for adrenal insufficiency was subsequently referred with a thyroid nodule and bilateral adrenal masses on pre-treatment 18F-FDG PET-CT (Figure 1A). Biopsies of the left thyroid nodule and adrenal masses confirmed the presence of synchronous papillary thyroid carcinoma and bulky diffuse large B-cell lymphoma, respectively. Central nervous system (CNS) involvement was excluded with contrast-enhanced MRI of the head and lumbar puncture, the latter performed for flow cytometry and CSF analysis. The patient was treated with six cycles of R-CHOP for bulky Stage IV lymphoma; treatment for the thyroid carcinoma was delayed pending completion of lymphoma therapy. CNS prophylaxis was administered in the form of intrathecal methotrexate. The patient went into complete metabolic remission; however, he only tolerated one cycle of intrathecal methotrexate therapy. Six weeks following the end of treatment 18F-FDG PET-CT, the patient presented with tongue deviation suggestive of a hypoglossal nerve palsy. Initial high-resolution MRI showed asymmetrical signal abnormality in the posterior tongue and floor of mouth, which was deemed to be indeterminate. CNS involvement was excluded, as above. The outcome of multidisciplinary meeting was a short-interval MRI. The patient was admitted 3–4 weeks later with a left tongue lesion. The mass and hypoglossal nerve demonstrated marked 18F-FDG uptake (Figure 1B); however, there was no disease elsewhere. Repeat MRI (Figure 2) demonstrated a 6 cm left hemi-tongue mass involving the sublingual and submandibular spaces with perineural extension along the ipsilateral hypoglossal nerve. Biopsy of the tongue mass returned aggressive B-cell lymphoma (high proliferation, CD-20 detected, overexpression of MYC protein, IGH:MYC fusion with translocation involving BCL6 consistent with double hit lymphoma). Given the early relapse, aggressive disease, rapid progression, and disease distribution with both extensive tongue infiltration and diffuse hypoglossal nerve infiltration, systemic therapy was considered more appropriate at Multidisciplinary Team Meeting discussion than salvage radiotherapy. The patient was commenced on dexamethasone and salvage chemotherapy with R-ICE chemotherapy, and complete metabolic remission ensued. Peripheral neurolymphomatosis (NL) is a rare complication of peripheral or cranial nerve root dysfunction that is most frequently secondary to infiltration by B-cell non-Hodgkin's lymphoma [1], though it may occur secondary to NK-cell or T-cell lymphomas or leukaemias. Presenting symptoms are variable, including plexopathy, foot drop, cranial nerve palsies, and radiculopathy, and diagnosis (radiological and pathological) can be difficult. This case emphasises the crucial role of high-resolution MRI ± 18F-FDG PET-CT in establishing the diagnosis and demonstrates the classic linear thickening seen along the hypoglossal nerve consistent with perineural tumour spread. Steroids alone provide short-term symptom control, and treatment is with chemotherapy. The authors have nothing to report.