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Diffuse Pulmonary 99mTc-MDP Uptake on Bone Scintigraphy: A Paraneoplastic Hypercalcemia Clue in Cervical Carcinoma
Address for correspondence: Dr. Ikram Zahfir, Department of Nuclear Medicine, Mohammed V Military Teaching Hospital, Rabat, Morocco. E-mail: ikramzahfir@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Wolters Kluwer - Medknow and was migrated to Scientific Scholar after the change of Publisher.
Abstract
99mTc-methylene diphosphonate bone scintigraphy is a cornerstone imaging modality for skeletal assessment; however, extraosseous radiotracer uptake may signal underlying systemic metabolic derangements. Diffuse pulmonary uptake, classically linked to metastatic calcification, is commonly observed in chronic kidney disease patients with calcium-phosphate homeostasis disruption. We present an uncommon case of bilateral pulmonary 99mTc-Methylene diphosphonate (MDP) uptake in a 48-year-old female with advanced cervical carcinoma, renal insufficiency, and severe hypercalcemia accompanied by paradoxically normal parathyroid hormone levels. While thoracic computed tomography showed no structural abnormalities, bone scintigraphy demonstrated diffuse pulmonary radiotracer accumulation, consistent with metastatic calcification secondary to calcium-phosphate deposition within alveolar walls. This case underscores the critical need for vigilant monitoring of metabolic complications in oncology patients, especially those with renal impairment, and highlights the diagnostic value of bone scintigraphy in identifying occult extraskeletal pathologies, even when conventional imaging appears unremarkable. The findings advocate for integrating metabolic profiling with functional imaging to better understand atypical tracer uptake patterns in high-risk populations.
Keywords
99mTc-MDP
bone scintigraphy
lung uptake
metastatic calcifications
A 48-year-old female patient with cervical carcinoma and a history of renal insufficiency was referred to the nuclear medicine department for disease staging. Whole-body bone scintigraphy, performed 3 h after the intravenous injection of 740 MBq (20 mCi) of 99mTc-MDP, revealed multiple skeletal metastases in addition to unexpectedly intense bilateral pulmonary uptake [Figure 1]. Blood tests confirmed hypercalcemia (corrected calcium: 169 mg/L) and normal parathyroid hormone (PTH) levels, along with elevated creatinine (24 mg/L), consistent with her pre-existing renal insufficiency. Thoracic computed tomography (CT) did not show any parenchymal lesions, except for a left pleural effusion [Figure 2]. These findings suggest a paraneoplastic metabolic disturbance, likely related to calcium-phosphate precipitation in the lungs due to prolonged hypercalcemia in the absence of elevated PTH.
Extraosseous radiotracer uptake in the thorax on bone scintigraphy may be associated with various malignant processes, including primary breast or lung cancers and malignant pleural effusions, as well as benign conditions, such as gynecomastia.[1] Diffuse pulmonary uptake can indicate metastatic calcification secondary to hypercalcemia, which is commonly caused by hyperparathyroidism, renal failure, or malignancy.[1] In this case, the findings were consistent with metastatic calcification, a phenomenon characterized by calcium-phosphate deposition in normal tissues during hypercalcemic states. Tissues with alkaline microenvironments, such as the lungs, gastric mucosa, and kidneys, are particularly susceptible to this process.[2] The patient’s paraneoplastic hypercalcemia is likely due to systemic osteoclast activation secondary to tumor-secreted factors, rather than direct bone marrow infiltration. While hypercalcemia in malignancy is often attributed to PTH secretion, our patient’s normal PTH levels and the absence of Parathyroid hormone-related protein (PTHrP) testing limit a definitive characterization of the underlying cause.[3] In addition, the absence of gastric uptake on scintigraphy and normal thoracic CT findings suggest a pulmonary-selective calcification process, likely driven by prolonged hypercalcemia in the context of renal dysfunction.[4]
In conclusion, this case underscores the importance of bone scintigraphy in detecting metastatic pulmonary calcifications, even when structural imaging, such as CT, appears normal, demonstrating its sensitivity to microcrystalline calcium-phosphate deposition. In addition, it highlights the need to consider paraneoplastic hypercalcemia in cancer patients presenting with unexplained extraosseous tracer uptake, especially when no primary skeletal pathology is identified.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Conflicts of interest
There are no conflicts of interest.
Nil.
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