Therapy-Induced Bone Marrow Activation
A significant percentage of patients presenting for PET/CT will have recently received chemotherapy and/or colony stimulating factors (CSF), both of which can lead to significantly increased metabolic activity of the bone marrow (and spleen, discussed here).
Regenerating bone marrow after chemotherapy causes diffuse reactive uptake throughout much of the axial and appendicular skeleton, often extremely intense. When colony stimulating factors are added to the treatment regimen, the increase in metabolic activity can be immediate and dramatic.
- If we see rather diffuse marrow uptake within 4 weeks of completion of chemotherapy and/or CSF administration and no CT evidence of osseous lesions, we consider this uptake “reactive” (some extend this up to 8 weeks after chemotherapy):
“There are no well-defined FDG-avid lytic or blastic bone lesions, although diffuse reactive marrow uptake on today’s study (presumably due to recent chemotherapy and/or colony stimulating factors) mildly limits evaluation of the skeleton.”
- In lymphoma patients, we are particularly wary of confusing extensive marrow infiltration with normal diffuse reactive marrow uptake. In these patients, we are especially careful to confirm an accurate history of recent therapy before dismissing this uptake as “reactive”.
In patients with a history of treated osseous metastases, scattered reactive marrow uptake may be mistaken for active hypermetabolic lesions, as adjacent treated lesions will be non-avid (“Flip-Flop Phenomenon”, discussed here ).
