A Pitfall We Should Be Aware of on Bone Scintigraphy

Introduction

Bone scintigraphy is a commonly used nuclear medicine imaging technique. It employs radiolabeled bone tracers to visualize osteoblastic activity and regional blood flow in the bones. This technique is highly sensitive and can detect both malignant and benign diseases, as well as various physiological processes. However, the presence of artifacts can lead to diagnostic confusion.

In this report, we present a case of inadvertent intra-arterial injection, which should be taken into consideration by physicians when interpreting results, particularly in cases of diffusely increased uptake observed in the extremities on delayed bone scintigraphy. It is essential for physicians to be aware of the possibility of injection artifacts, which can mimic or mask pathology, and may lead to misdiagnosis or incorrect treatment.

Case Report

A 52-year-old female patient with invasive ductal carcinoma of the left breast (estrogen receptor-negative, HER2-positive with lymph node metastases) underwent left mastectomy with homolateral axillary lymph node dissection and adjuvant chemotherapy (three cycles of 5-fluorouracil, epirubicin, and cyclophosphamide and three cycles of docetaxel), radiation therapy, and monthly trastuzumab injections on the dorsum of the right hand. A bone scintigraphy for initial extension assessment performed 19 months ago had been normal. The patient reported low back pain. Computed tomography scan and phosphocalcic blood testing revealed no abnormalities. She was referred to a nuclear medicine department for a follow-up bone scan.

The patient was injected with 740 MBq of ^99mTechnetium hydroxymethylene diphosphonate into a blood vessel in the right antecubital fossa. After 2 h, whole-body imaging showed a diffuse increased uptake on the right forearm and right wrist–hand [Figure 1]. Additional static views revealed the same radiotracer uptake, which was significant on the radius, cubitus, wrist, and the radial half of the hand [Figure 1]. The patient had no history of trauma or specific symptoms. The tourniquet was applied above the elbow but only for 10 s. There was no extravasation of radiotracer in the images. Three weeks later, three-phase bone scintigraphy was performed, and the radiotracer was injected into the antecubital vein of the opposite arm. No abnormality was detected in all the three phases [Figure 2].

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Figure 1 Anterior whole-body scintigraphy (a) and dorsal static view (b) showing increased bone uptake in the right forearm–wrist–hand (arrow)

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Figure 2 (a) Anterior whole-body scintigraphy of reevaluation. (b) Dorsal static views showing symmetrical uptake on the three-phase bone scintigraphy

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Discussion

Our case exhibits an increased uptake of the right upper limb. Various diagnoses were considered to explain the scan findings, including metastasis, complex regional pain syndrome (CRPS),[1] Raynaud’s phenomenon,[2] infective disorder,[2] tourniquet effect,[3] frostbite injury,[4] radiotracer extravasation,[5] or a probable effect of trastuzumab injections. There was no clinical proof of CRPS, infective disorder, or Raynaud’s phenomenon. Direct signs of local extravasation and lymphatic/interstitial migration were not visible in our patient. Tourniquet effect and frostbite injury were ruled out by clinical history. In addition, the image patterns did not fit the description of metastasis. However, a three-phase bone scan was suggested for confirmation. We, then, concluded that the increased uptake was caused by intra-arterial injection of the radiotracer into the radial artery.

Few case reports reported the intra-arterial injection of radiolabelled bone tracers; Shih et al.[6] described the incidental arterial injection of the tracer into the antecubital fossa as “glove” phenomenon, where there is increased uptake in the wrist and hand bones, as well as in the soft tissue of the distal forearm. Giammarile et al.[7] reported a case of intra-arterial injection involving the venous system of the foot. By analogy with the "gauntlet" (or "glove") sign, they suggested naming this new finding the "sabaton" (or "sock") sign. The underlying physiopathology of this sign could be explained by the increased blood flow in the arterial system at the first step of the radiotracers binding mechanism.[4]

Conclusion

For the most accurate interpretation, physicians must be aware of the patient’s medical history, physical examination, and technical challenges before and during bone scintigraphy. They should be aware of injection pitfalls that may be responsible for increased bone uptake and simulate pathological processes. In some cases, this may spare the patient from needless invasive testing or biopsy.