Case report: positive pitfalls of PSMA PET/CT: diagnostic challenges in degenerative bone lesions including MODIC type 1

Prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) is an imaging technique that has demonstrated high sensitivity and specificity in detecting prostate cancer and its metastasis, especially in the bones. This case describes a 60-year-old man who presented for increased prostate-specific antigen (PSA) level and underwent [⁶⁸Ga]gallium-PSMA-11 PET/CT imaging for better disease assessment. ⁶⁸Ga-PSMA-11 PET/CT revealed numerous radiotracer-positive lesions in both prostate lobes with associated sclerotic lesions on L4 and L5, but only L5 showed increased radiotracer avidity raising the possibility of metastasis. Magnetic Resonance Imaging (MRI) raises the possibility of aggressive MODIC type 1 lesion vs. infectious/inflammatory process. A biopsy of the radiotracer avid area was performed and showed no evidence of metastasis. The final diagnosis was aggressive MODIC type 1, in keeping with the false positive result of ⁶⁸Ga-PSMA-11 PET/CT. This example demonstrates the possible limitations of ⁶⁸Ga-PSMA-11 PET/CT, particularly in detecting bone metastases, and emphasizes the need for cautious interpretation and additional study to improve its diagnostic accuracy. Understanding and resolving these limitations is critical for increasing the accuracy of PSMA PET/CT in prostate cancer management.

1 Introduction

Prostate-specific membrane antigen (PSMA) is a non-secreted transmembrane protein expressed in prostate tissue and tumor-related blood vessels. PSMA uptake has been observed in a variety of tumors and benign diseases (1, 2). Nevertheless, PSMA has shown the most promise in the detection and staging of prostate malignancy and is now considered the optimal imaging technique in the diagnosis of prostate cancer (3, 4). In a meta-analysis of seven studies compromising 389 patients undergoing initial diagnosis of prostate cancer, PSMA positron emission tomography/computed tomography (PET/CT) demonstrated a pooled sensitivity and specificity of 0.97 and 0.66, respectively, with a positive likelihood ratio of 2.86 and negative likelihood ratio of 0.05 demonstrating that PSMA PET/CT is a useful technique for excluding malignancy in patients with clinical suspicion of prostate cancer, thus avoiding unnecessary biopsies (5).

Prostate cancer is known to spread to cortical bone and bone marrow, contributing to the majority of prostate cancer-related fatalities. While bone scans are used to detect osteoblastic skeletal metastases, they lack specificity to distinguish between benign and malignant lesions (6). Combini