18F-Fluoride bone positron emission tomography demonstrating changes related to finger clubbing and hypertrophic osteoarthropathy.

Hypertrophic pulmonary osteoarthropathy is manifested by clubbing and periostitis of bones. We present a very rare documentation of increased F18-sodium fluoride uptake in the distal phalanges of both hands correlating to clubbing of the fingers in a 55-year-old female patient with carcinoma of lung in whom bone positron emission tomography was performed for metastatic work-up.

A 55-year-old female patient with carcinoma of the lung was subjected to positron emission tomography (PET) bone scan for metastatic work-up. F18-sodium fluoride (NaF) bone PET carried out 60 min after intra-venous injection of 340 MBq of 18F-NaF on a PET/computed tomography (CT) scanner (GE Discovery ST600, Milwaukee, USA) showed metastatic foci in cervical and dorsal vertebrae [Figure 1a]. Tram-track appearance is seen in the femur on both sides is indicative of hypertrophic osteoarthropathy (HOA) (curved arrow). Image [Figure 1b] also demonstrates increased fluoride uptake in the distal phalanges of both hands (arrows). Clinical photograph [Figure 1c] shows finger clubbing. Fused axial PET CT images showing increased fluoride uptake in the phalanges and uptake along the femur. The additional advantage of F-18 NaF bone PET is, being a whole body imaging procedure, the modality demonstrated changes along the femur apart from the metastatic sites in the vertebral column in this particular case.

Figure 1

(a) Maximum intensity projection image of F18-fluoride bone positron emission tomography (PET) done 60 min after intra-venous injection of 340 mBq of 18F-sodium fluoride on a GE Discovery ST600 PET/computed tomography (CT) (Milwaukee, USA) demonstrate, metastatic foci in cervical and dorsal vertebrae. Tram-track appearance is seen in the femur on both sides is indicative of hypertrophic osteoarthropathy (curved arrow). Image also demonstrates increased fluoride uptake in the distal phalanges of both hands (arrows). (b) Clinical photograph showing finger clubbing. (c) Fused axial PET CT images showing increased fluoride uptake in the phalanges and uptake along the femur

HOA is seen in approximately 1% of cases of lung cancer.[1] Clubbing is an intrinsic feature of HOA. The increased uptake in the long bones is secondary to periostitis induced osteoblastic activity.[2] The increased vascularity and soft-tissue proliferation with erosion of the distal phalanges[3] induced by platelet derived growth factor and vascular endothelial growth factor result in increased tracer uptake in the distal phalanges. Demonstration of changes of clubbing has been documented on 18F-fluorodeoxyglucose studies[4567] and on conventional bone scan with fusion imaging.[8910] F18-NaF bone PET has been demonstrated through-out the literature to be more sensitive than conventional bone scan with technetium 99 m – methylene diphosphonate. This is due to the fact that uptake of NaF like other bone agents is dependent on blood flow and osteoblastic activity. Fluoride is adsorbed onto the surface of bone in exchange for hydroxyapatite. However, it is characterized by 2-fold higher uptake, faster clearance from blood and better target to non-target ratio.[1112] The addition of CT component to the PET increases its specificity for interpretation of findings.[1314] We present a very rare documentation of clubbing related changes on F18-NaF study.