Deleveaux, S.

Abstract Introduction Medullary thyroid cancer (MTC) is an uncommon malignancy arising from the C-cells of the thyroid gland. It makes up 2% of all thyroid cancers, with both familial and sporadic patterns noted. It is most commonly diagnosed in the fourth to sixth decade of life, with the lungs being a common site of metastasis. We present a case of metastatic MTC with a rare pulmonary presentation. Case Description The patient presented at the age of 28 after having a chronic complaint of stomach pain and diarrhea. Imaging of the abdomen revealed small nodules in the lower pulmonary fields. Dedicated imaging of the chest was subsequently ordered. This study was notable for an enlarged left lobe of the thyroid extending into the mediastinum with two large mediastinal lymph nodes. A fine-needle aspiration of the left neck lymph node was consistent with MTC and there were hematologic findings of elevated calcitonin and CEA. Testing for the RET proto-oncogene was negative. Pathology on total thyroidectomy confirmed the diagnosis, with further sampling identifying metastasis in the thoracic spine (T12). Initial therapy with pazopanib was commenced. After some time on stable therapy, the patient was noted to have waxing and waning pulmonary micro-nodularity associated with increase in his calcitonin levels. There was a finding of a miliary pattern of disease on chest imaging. The pulmonary service was consulted due to these findings in conjunction with sub-acute cough. Pulmonary biopsy was performed, with findings of nodular amyloidosis; Congo red stain highlighted amyloid deposition. Immunohistochemical studies were performed, revealing rare cell groups that were positive for calcitonin, CEA, CAM5.2, TTF-1, chromogranin, and synaptophysin. After further discussion with the Pathology service, the patient was given formal diagnosis of amyloid deposition of the Acal subtype due to metastatic medullary thyroid cancer. Discussion This case highlights a patient diagnosed with sporadic MTC, later found to have metastatic related pulmonary amyloid deposition. While local amyloid deposition can be seen in MTC, it is unusual to have diffuse parenchymal disease due todiffuse parenchymal disease due to distant deposition. There are only four other instances in the literature of a similar presentation. Amyloid deposition is associated with worse outcomes, but the patient had a good outcome with treatment by a tyrosine-kinase inhibitor.

Abstract Rationale: Lymphoid Interstitial Pneumonia (LIP) is a rare interstitial lung disease characterized as a benign lymphoproliferative pulmonary condition. It is often associated with autoimmune conditions such as Sjögren's syndrome, immune dysregulatory syndromes, and common variable immunodeficiency. The incidence and prevalence of LIP remain unclear. While fluorodeoxyglucose (FDG) Positron Emission Tomography (PET/CT) findings have been documented for various diffuse parenchymal lung diseases, data specific to LIP is limited. This study aims to assess the utility of PET/CT in the evaluation of malignancy in patients with LIP, in addition to describing PET/CT findings in patients with known LIP who underwent PET/CT for any reason. Methods: This retrospective study involved a reviewof electronic medical records within the Mayo Clinic Enterprise to identify patients with an established diagnosis of LIP who had undergone PET/CT. Using ICD code J84.2, we identified patients with a diagnosis of LIP, and further selected for those who had undergone PET/CT between 2009 and 2023. We analyzed descriptive statistics, including the mean and prevalence of common PET/CT findings. Results: We identified 10 patients, all of whom had anestablished expert diagnosis of LIP and had undergone PET/CT for any reason. The mean age was 66 years, and all patients were female. Six of the ten patients (60%) underwent a lung biopsy, and six (60%) exhibited FDG uptake in the lungs, with maximum standard uptake value (SUVmax) uptake ranging from 2.0 to 8.2. Six of the imaging studies (60%) showed abnormal FDG uptake in one or more lymph nodes, with SUV maximum ranging from 2.4 to 7.8, and four (40%) demonstrated extrapulmonary FDG uptake. Four patients were diagnosed with a malignancy, the majority being MALT, with one being lung squamous cell carcinoma (SCC). Conclusion: Given the rarity of LIP, there is limiteddata on the utility and findings of PET/CT in these patients. Our study reveals that in patients with LIP, despite abnormal parenchyma in the background of inflammatory disease, malignancy was still likely in abnormally hypermetabolic regions. In this study, lymphoma was the most common malignancy isolated in patients with LIP. Nonetheless, malignancy other than lymphoma can occur, namely squamous cell carcinoma (SCC), and PET positivity can occur in LIP patients even in the absence of tissue proven malignancy. In patients with LIP, SUVmax does not appear to be a differentiating factor between those later diagnosed with lymphoma (SUVmax 2.0-8.2) and SCC (SUVmax=3.1).