Pam McKay

Bone marrow signal during PET imaging in Hodgkin lymphoma

Positron emission tomography (PET) has added considerably to the management of Hodgkin lymphoma (HL). PET is of value in staging disease, response assessment and evaluation of a residual mass post-treatment. Full staging of advanced disease has traditionally required a bone marrow biopsy and this is still considered standard practise, although some authors argue that this rarely alters patient management. It had been hoped that the use of PET imaging at diagnosis would clearly define bone marrow involvement in HL and remove the need to perform bone marrow biopsies. It is clear, however, that PET cannot readily differentiate between ‘reactive’ and ‘involved’ bone marrow when the PET signal is diffusely increased in bone. The substrate, 2-fluoro-2-deoxyD-glucose (FDG), is readily taken up by metabolically active tissue and a reactive bone marrow with expansion of myeloid and lymphoid activity can show a degree of uptake very similar to that of bone marrow involved by disease. The first image (left) shows the FDG-PET signal from a patient with HL with a reactive bone marrow biopsy at diagnosis. The diagnosis of a reactive bone marrow was made from a single iliac crest bone marrow biopsy in association with a normocytic anaemia, neutrophilia and raised erythrocyte sedimentation rate. The second (centre) shows the FDG-PET signal from a patient with Stage 4 HL with heavy bone marrow infiltration shown by biopsy at diagnosis. The third (right) shows a normal bone marrow FDG-PET signal for comparison. PET is an invaluable imaging tool used in the assessment of patients with HL. However, it should be used to compliment bone marrow trephine biopsy, rather than replace it, if patients are to be accurately staged prior to therapy.