Incidental detection of axillary lymph node metastasis from carcinoma breast during technetium-99m methoxyisobutylisonitrile parathyroid scintigraphy

Sir,

We describe a suspected case of primary hyperparathyroidism with brown tumors where on parathyroid scintigraphy, an incidental finding of hyper-metabolic lesion in the right axilla, was noticed which was later on confirmed to be metastasis from breast cancer. A 61-year-old-female patient presented with back pain for 6 months duration. She had hypercalcemia and elevated serum alkaline phosphatase levels. X-ray of the skull and pelvis showed multiple lytic lesions which raised the suspicion of primary hyperparathyroidism with brown tumors. Technetium- 99m methoxyisobutylisonitrile (MIBI) parathyroid scintigraphy [Figure 1a and b] was negative for parathyroid adenoma; however, a hypermetabolic lesion in right axilla was noted. Single photon emission computed tomography/computed tomography (SPECT/CT) localized the uptake to the right axillary lymph node (arrows on CT and SPECT/CT images). It also showed multiple lytic lesions in cervico-dorsal vertebrae. Scintigraphic impression of metastatic right axillary nodal involvement was made. Keeping the probability of primary malignancy in breast, she was further subjected to mammography which on Breast Imaging-Reporting and Data System (BIRADS) showed BIRADS 5 on right side and BIRADS 2 on left side. Ultrasound of the breast revealed a heterogenous hyperechoic lesion of size 9 mm × 5 mm which was not palpable on clinical examination. Ultrasound guided fine needle aspiration cytology reported lesion in right breast as carcinoma infiltrating duct and from right axillary lymph nodes as metastasis. Whole body bone scan with technetium-99m methylene diphosphonate (MDP) revealed increased osteoblastic activity in multiple bones suggestive of wide spread skeletal metastasis [Figure 1e and f].

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Figure 1 Technetium-99m methoxyisobutylisonitrile parathyroid scintigraphy [(a) early image; (b) washout image] negative for parathyroid adenoma showing a hypermetabolic lesion in right axilla. Single photon emission computed tomography/computed tomography (SPECT/CT) localized the uptake to the right axillary lymph node (arrows on CT (c) and SPECT/CT (d) images). Technetium-99m MDP whole body bone scan (e and f) revealed increased osteoblastic activity in multiple bones suggestive of wide spread skeletal metastases

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The uptake mechanism of Tc99m-MIBI involves passive diffusion across plasma and mitochondrial membranes and at equilibrium it is sequestered within mitochondria by the large negative transmembrane potentials.[1] Studies have confirmed the relationship between cellular uptake of MIBI and mitochondrial activity or density.[2] The multi-drug-resistant P-glycoprotein system uses MIBI as a substrate and effectively transports it out of tumor cell.[3] The overall concentration of Tc99m MIBI in tumors is a function of many variables including factors that affect the rate of uptake and that determine wash out or excretion from the cell.[4] Tc99m-MIBI uptake in axillary lymph nodes could be due to involvement of lymphoma,[5] metastases of breast malignancy,[6] and extravasated radioactivity in the ipsilateral upper limb.[7] There have been studies evaluating the role of scintimammography using Tc99m MIBI for evaluation of primary carcinoma of breast and axillary lymph node metastasis.[89] Hypermetabolic lesion in axilla as an incidental finding in planar parathyroid scintigraphy with localization to lymph nodes on SPECT/CT in this suspected case of primary hyperparathyroidism with brown tumors has helped in further evaluation for breast cancer. Subsequently, it was confirmed to be a case of breast carcinoma with axillary lymph nodal and bone metastases with hypercalcemia of malignancy. The findings had essentially changed the diagnosis and hence the management of the patient.