Toxic multinodular goitre identified at vascular and late phase of Tc99m MDP bone scan

An 82-year old female patient was referred to our department for Bone Scan (BS) for differential diagnosis of soft tissue infection at amputation site. Vascular phase and whole body BS revealed focally increased thyroid uptake in the left neck. Multinodular goiter with internal micro and macrocalcifications were apparent in neck ultrasonography. 99mTc pertecnethate scintigraphy confirmed focally increased uptake with hypoactive areas probably due to cystic/necrotic field in toxic nodules. The patient’s thyroid function tests were as follows; TSH <0.003 μIU/mL, sT3 3,23 μg/mL, sT4 0,88 ng/mL. The history of patient and thyroid function tests supported diagnosis of toxic multinodular goiter. Correspondence to: Murat Sadıc, M.D, Department of Nuclear Medicine, University of Health Sciences, Ankara Training and Research Hospital, Turkey, Tel: +903125953608; Fax: +90 312 595 38 56; E-mail: mdmuratsadic@ gmail.com


Introduction 99m
Tc Methylene Diphosphonate (MDP) uptake in extraosseus areas is unexpected but it is clinically important. MDP acts as ligand adsorbing onto tissue calcium, localizing the 99m Tc in the mineral phase with no significant organic subtrate interaction. The general mechanism of 99m Tc MDP uptake is binding to hydroxyapatite crystals and calcium salts causing the skeletal accumulation and uptake in the other of calcium deposition in the body. In this case, we presented an 82-year old female patient who was referred to our department for Bone Scan (BS) and had focally increased thyroid uptake in the left neck at vascular phase and whole body BS.

Case presentation
An 82-year old female patient was referred to BS for diagnosis of soft tissue infection and osteomyelitis at amputation site. After regional dynamic and blood pool images at amputation site, vascular phase of the whole-body scan has shown incidental hyperemia and whole body Bone Scan (BS) presented thyroid uptake at the left lower neck. Vascular phase and whole body BS revealed focally increased thyroid uptake in the left neck.
Thyroid ultrasonography showing the nodule in the left lobe which fills left lobe nearly complete (34×22 mm in size) with cystic, necrotic field with internal multiple micro and macrocalcification within highly increased vascularity of the nodules. Multinodular goiter with internal micro and macrocalcifications were apparent in neck ultrasonography. The findings were consistent with toxic multinodular goiter. 99m Tc pertecnethate scintigraphy confirmed focally increased uptake with hypoactive areas probably due to cystic/necrotic field in toxic nodules. The patient's thyroid function tests were as follows; TSH <0.003 µIU/ mL, sT3 3,23 µg/mL, sT4 0,88 ng/mL. The history of patient and thyroid function tests supported diagnosis of toxic multinodular goiter.

Discussion
In our case, it was the vascular phase of the whole-body scan showing focally intense hyperemia in the toxic nodules even though MDP uptake in thyroid in bone phase was also apparent. In our department, we obtain whole body scan of BS patients in vascular phase to evaluate the alterations in bone modeling profoundly and for any incidentally information about the patient that might be important without any additional radiation dose. MDP uptake in extraosseus areas is unexpected but it is clinically important. Recent research indicated that MDP acts as ligand adsorbing onto tissue calcium, localizing the 99m Tc in the mineral phase with no significant organic subtrate interaction [1,2]. The general mechanism of 99m Tc MDP uptake is binding to hydroxyapatite crystals and calcium salts causing the skeletal accumulation and uptake in the other of calcium deposition in the body [3,4]. In our case, increased 99m Tc MDP uptake in the thyroid nodules was possibly caused by calcifications of the nodules (Figure 1). 99m Tc pertecnethate scintigraphy confirmed focally increased uptake with hypoactive areas probably due to cystic/necrotic field in toxic nodules ( Figure 2). Regarding Kurooka et al., classification of thyroid cartilage uptake in BS, our case has slight inhomogeneous accumulation in thyroid cartilage, which was the most common pattern in BS [5] (Figure 3).

Conclusion
Vascular phase whole body screening should be complementary to regular BS which may be very useful and give additional information about diagnosis of other diseases and allow early detection [6]. Clinician especially nuclear medicine physicians should be aware that incidental thyroid nodules may demonstrate 99m Tc MDP accumulation probably due to calcification in nodular area on BS [7].