Histoplasmosis and Sarcoidosis mimicking metastatic disease on FDG positron emission tomography

Abstract

2117 Introduction: Positron emission tomography (PET) has come to play an increasingly important role in the evaluation of cancer patients, both for diagnostic as well as post treatment follow-up. Like other techniques, PET is associated with false positive and negative Results: False positives have been reported in presence of active granulamatous diseases like tuberculosis, aspergillosis, histoplasmosis. We report 2 such cases. Case 1: A 74-year-old male presented with abdominal pain requiring emergency laparotomy that revealed a stricture in jejunum, biopsy of the specimen confirmed diffuse large B cell lymphoma. The patient received CHOP chemotherapy and rituxan. A PET scan performed as treatment follow-up showed progression of the disease in the mediastinum with increased metabolic activity of the lymph node (LN) that had grown in size from 9 mm to 12.5-mm. In addition there were multiple new small LNs in the mediastinum. The patient underwent mediastinoscopy and subsequent biopsy of LN that was negative for malignancy. Further work-up revealed that enlarged LN was due to sarcoidosis. Case 2: A 46-year-old-female with a history of left infiltrating ductal carcinoma of the breast, treated with lumpectomy, radiation and tamoxifen therapy, underwent a follow-up PET scan that showed an anterior pleural based 10x 16 mm nodule in the right middle lobe that demonstrated moderately intense abnormal hypermetabolic activity and 3 hypermetabolic foci present in the right hilum. Differential diagnosis included primary lung carcinoma with right hilar metastasis or metastatic breast cancer. Patient underwent right middle lobe resection that was negative for malignancy. It revealed necrotizing granulomatous inflammation with budding yeast suggestive of histoplasmosis. Conclusion: PET scans play a very important role in the staging of various malignancies and treatment follow-up. However, as demonstrated in these 2 cases, caution should be exercised especially when PET scan findings are used to alter treatment plans. In these situations, tissue diagnosis is mandatory in order to establish accurate diagnosis and avoid potentially toxic therapeutic interventions such as chemotherapy and radiotherapy. No significant financial relationships to disclose.