A case report on metastatic prostate cancer with normal PSA level diagnosed by immunohistochemistry and its management.

Introduction and importance: Metastatic prostate cancer (mPCa) is an advanced form of cancer that spreads beyond the prostate to distant organs such as bones and lymph nodes. While prostate-specific antigen (PSA) testing is commonly used for diagnosis, rare cases with normal PSA levels complicate detection. This case highlights the crucial role of immunohistochemistry (IHC) in diagnosing mPCa with normal PSA and its management in resource-limited settings. Case presentation: A 63-year-old male presented with 2 months of persistent back pain without neurological deficits. Initial diagnostics, including PSA levels, CT, MRI, and TRUS guided prostate biopsy, revealed no prostate abnormalities. However, an MRI and Bone scan showed a suspicious vertebral lesion, and a subsequent biopsy confirmed malignancy. IHC demonstrated overexpression of alpha-methyl acyl-CoA racemase (AMACR), leading to the diagnosis of mPCa. The patient underwent bilateral subcapsular orchiectomy and received external beam radiotherapy (EBRT) to manage symptoms and control disease progression. Clinical discussion: This case highlights the diagnostic challenges of mPCa in patients with normal PSA levels. Standard diagnostics, including imaging and biopsy, may fail to detect prostate cancer, making IHC, specifically AMACR, an essential tool for diagnosis. Early surgical intervention followed by EBRT offered significant symptomatic relief and disease control. Conclusion: This case demonstrates the importance of IHC in diagnosing atypical presentations of mPCa with normal PSA. A multidisciplinary approach combining surgery and radiotherapy can improve outcomes and quality of life, even in resource-limited settings.