Abstract
2787
Introduction: Adequate staging of paediatric patients with Langerhans Cell Histiocytosis (LCH) is important in characterising patients with high-risk vs low-risk LCH, of which the former carries a higher mortality and morbidity. Conventional Imaging (CI) modalities such as skeletal survey, bone scan, CT and MRI have been utilised to a greater extent in staging of LCH. Over the last decade 2-deoxy-2-[18F]fluoro-D-glucose(2-[18F] FDG) positron emission tomography/computed tomography (PET/CT) has been shown to be more accurate in characterising active lesions at staging and response assessment in bone and soft tissue when compared to CI. Bone marrow biopsy (BMB) is part of the routine diagnostic work up in LCH for detecting bone marrow involvement (BMI) which apart from being invasive and requiring anaesthesia, may be hampered by inadequate sampling techniques. In Hodgkin’s lymphoma, it has been shown that if 2-[18F] FDG PET/CT is performed that an additional BMB is not required for staging.
Aim:
The primary aim of the current study was to correlate BMB and PET/CT results at initial staging/restaging of LCH and to assess whether 2-[18F] FDG PET/CT could potentially eclipse BMB as a staging modality with LCH.
Methods: 2-[18F] FDG PET/CT staging/restaging studies were observed retrospectively between 2013 and 2021. Patients with confirmed LCH who were CD1a and S100 positive on histology were included. Patients who did not have BMB as part of their routine workup were excluded. Reports and images were reviewed. The SUVmax, SUVmean of the bone marrow(BM) and SUVmean of the liver(L) were recorded. The ratio between SUVmean of the bone marrow and SUVmean of the liver was also recorded (BM/L).Bone marrow involvement (BMI) was defined as positive if (1) this was confirmed on the BMB report or (2) there were single/multiple foci of pathological uptake on 2-[18F] FDG in the skeleton which either disappeared or progressed on subsequent studies. The number and location of the skeletal uptake and corresponding CT changes were recorded. The stage of disease and organs at risk were recorded.
Results: The study included 13 studies in nine patients (median 2.84 years, range 0.25 – 11.8 years). Six (46%) patients had confirmed multi-system (MS)-LCH: four in ‘risk’ organs (spleen and lung) and two in non-risk organs (lymph nodes).
Of the 13 studies, six (46%) confirmed BMI on 2-[18F] FDG PET/CT. Three studies (23%) were confirmed positive for BMI on BMB. Both 2-[18F] FDG PET/CT and BMB were positive in three patients.
Twenty-four sites of skeletal uptake were identified in six patients. Sixteen (67%) of these lesions were 2-[18F] FDG avid. There were eight lesions that did not show FDG avidity, they were limited to the skull. CT changes were seen in all identified skeletal lesions.
When comparing the performance of 2-[18F] FDG to BMB for BMI detection, 2-[18F] FDG had a higher sensitivity when compared to BMB (100% vs 50%).
Conclusions: The current study suggests that 2-[18F] FDG detection of BMI was more sensitive than BMB and could potentially obviate the need for routine BMB at diagnosis. This finding requires validation in a larger cohort of patients.
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