Utility of F-18 Fluorodeoxyglucose Positron Emission Tomography-Computed Tomography in a Patient Presenting with Acute Paraparesis in Detecting Isolated Relapse of Non-Hodgkin's Lymphoma Infiltrating the Spinal Cord

Sir,

We report the case of a 62-year-old woman – a diagnosed case of diffuse large B-cell lymphoma (DLBCL) Term Stage IV BX, involving multiple lymph nodes on both sides of the diaphragm along with liver and skin lesions – who achieved remission with six courses of Rituximab, Vincristine, Cyclophosphomide, Doxorubicin, Prednisone (R-CHOP). Two years later, she complained of continuous low backache radiating along the back of both the thigh. The pain was associated with progressively increasing bilateral lower-limb weakness. Examination revealed normal higher mental functions, normal power of the upper limbs (5/5), and decreased power of the bilateral lower limbs (3/5). Bilateral knee and ankle reflexes were brisk and mute, respectively. Biochemical and hematological parameters were normal except leukocytosis (15,300; normal: 4000–11,000/cm ³). Magnetic resonance imaging (MRI) lumbosacral spine T1-weighted [Figure 1a] and T2-weighted images [Figure 1b] showed altered signal in the lumbar thecal sac with clumping of the caudal nerve roots in almost whole of the lumbar spine, partially encasing the conus part of the cord and complete cerebrospinal fluid (CSF) effacement in the lumbar thecal sac [Figure 1a and b]. CSF cytology from the subarachnoid space revealed lymphomatous cells. In view of the clinical suspicion of disease recurrence, ¹⁸F fluorodeoxyglucose positron emission tomography and computed tomography (¹⁸F-FDG PET/CT) was done, which showed midline, linear increased FDG uptake in the spinal column of the dorso-lumbar region in maximum intensity projection image [Figure 2a]. The corresponding sagittal and transaxial contrast-enhanced computed tomography and fused images [Figure 2b-e] revealed linear intense tracer avidity (maximum standard uptake value 16.8) in the lobular dorso-lumbar spinal cord extending below the conus till the level of L4 vertebra. The patient was put on steroids and received radiotherapy, and she showed immediate symptomatic improvement.

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Figure 1

T1- (a) and T2-weighted (b) magnetic resonance imaging images showing altered signal in the lumbar thecal sac with clumping of the caudal nerve roots in almost whole of the lumbar spine, partially encasing the conus part of the cord and complete cerebrospinal fluid effacement in the lumbar thecal sac

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Figure 2

¹⁸F fluorodeoxyglucose positron emission tomography and computed tomography maximum intensity projection (a), sagittal computed tomography (b), sagittal fused positron emission tomography/computed tomography (c), axial fused positron emission tomography/computed tomography (d), and axial computed tomography (e) images showing midline linear increased tracer uptake in the spinal column of the dorso-lumbar region (arrow a). The increased fluorodeoxyglucose uptake corresponded to the uptake in lobular dorso-lumbar spinal cord extending below the conus till the level of L4 vertebra (c, arrow)

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DLBCL frequently presents as disseminated disease at the time of diagnosis though the standard treatment of R-CHOP therapy has improved the outcome significantly.[1] Following first-line therapy, 50%–60% of the patients achieve complete remission, whereas the remaining 10% and 30%–40% have refractory disease and relapse, respectively.[2]

Unfortunately, in the first 2–3 years, patients with DLBCL relapse after treatment, with the extranodal sites being more frequently involved than the nodal sites. Imaging studies help in the identification of the location of relapse. Various unusual sites of relapse of lymphoma such as trachea, orbit, meninges, and terminal ileum have been described in literature.[3]

Secondary involvement of the spinal cord in DLBCL is extremely rare. In Mayo Clinic patient database of 14 years, only seven patients of non-Hodgkin's lymphoma (NHL) with a median age of 61 years and subacute presentation were found to have secondary intramedullary spinal cord involvement on CSF cytology, FDG PET, and MRI. Majority of them had myelopathy following the diagnosis of NHL with favorable survival posttreatment. These patients usually have early neurological morbidity. MRI spine, ¹⁸F-FDG PET/CT, and CSF cytology help in the identification of disease and its management.[4] Whole-body ¹⁸F-FDG PET/CT assists in the identification of the other sites of lymphomatous involvement for staging of the disease and response evaluation after intervention. Patients in whom CSF sampling is difficult/unsafe to obtain or unable to undergo MRI scan for various reasons may be benefitted from 18F-FDG PET/CT which can help in detection of spinal cord involvement and timely treatment with favourable survival outcome.