Role of FDG PET/CT scan in suspected neuro-lymphomatosis: An area of supremacy?

Introduction: Neurolymphomatosis is rarely encountered in high-grade lymphomas. It is due to malignant lymphocytes infiltrating the endoneurium. Due to non-specific symptoms, it has to be differentiated from post-chemotherapy-induced neuro-toxicities, radiation-induced plexopathy, inflammatory neuritis, compression neuropathy, and paraneoplastic syndrome. Contrast-enhanced MRI is the investigation of choice for neuropathic symptoms albeit its non-specific features. FDG PET/CT is the investigation of choice for high-grade lymphoma workup. Here, we presented the role of FDG PET/CT in suspected cases of neuro-lymphoma.

Methods: We retrospectively analyzed 328 high grade lymphomas cases done in 2020-2022 and six cases of neuro-lymphomatosis were identified. These cases were analyzed to look for possible risk factors, common and uncommon presentations, incremental value and the lessons learned by FDG PET/CT scan.

Results: Neuropathic pain was the most common symptom with mono or polyradiculopathy in our series. However, all lymphomatous infiltrated nerves diagnosed on FDG PET/CT were not symptomatic. This was the major challenge for MRI to decide the area of imaging. The lumbar, brachial plexus and trigeminal nerve were the most common sites and were well depicted on FDG PET/CT. MRI of the brain better delineate cranial nerves and meningeal involvement. CSF flow cytometry was normal until meninges were involved. FDG PET/CT incrementally evaluated extra-neural disease sites, thus helped in deciding biopsy site and further management. It also helped in post chemotherapy response assessment.

Conclusions: We concluded that a whole-body FDG PET/CT better delineate extent of peripheral nerves, while MRI CNS involvement. Hence, a whole-body PET/CT scan including limbs with MRI brain was the appropriate investigation for evaluating suspected neurolymphomatosis. Extra-neural disease, guidance for biopsy and response assessment were also the supreme areas of it.

Figure 1: FDG PET/CT maximum intensity projection (a), axial (b, d), sagittal (c), and coronal (e) fused images. Metabolically active left L5-S1 sciatic nerve roots (block arrows, image a, e), right trigeminal nerve (arrows, image a, b, c), and left adrenal (curved arrow, image d) involvements. A left adrenal biopsy confirmed recurrence.

Learning points Neurolymphomatosis usually has multifocal involvement with different degrees of symptoms. Extraneural disease may present along, which may be a better site for biopsy. As in this case, the patient was symptomatic of left sciatic nerve; however, the involvement of the right Vth CN and left adrenal gland was also noted, which implied the management decision.

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