Case Presentation: An 82-year-old male with history of urinary retention, presumed to be due to benign prostatic hypertrophy, requiring a chronic indwelling Foley catheter presented with progressively worsening non-mechanical back pain of four-month duration. All vital signs were within normal limits. Physical exam was notable for bilateral crackles and suprapubic tenderness. As patient had presented the emergency department multiple times in the previous several months for multiple complaints including persistent suprapubic pain, lower back pain, and flank pain, CT of the abdomen and pelvis without contrast was obtained which revealed sclerotic bone lesions on right ilium and left pubic ramus, a L1 compression fracture, and multiple nodules bilaterally at the lung bases. Subsequent CT of the chest revealed innumerable bilateral pulmonary nodules with largest measuring 3.6 x 2 cm, and numerous enlarged and calcified mediastinal and hilar lymph nodes. Laboratory data was notable for PSA of 10.94 ng/mL (normal <6.50 ng/mL). Further workup including MRI of the spine re-demonstrated right iliac sclerotic bone lesion. Due to concerns for metastatic cancer, biopsy of the right iliac sclerotic lesion was obtained, which returned negative for malignancy. Subsequently, patient underwent a core biopsy of the large lung mass, which revealed fibrosis with anthracotic pigment and polarizable particles consistent with pneumonicosis. Upon further questioning, patient later disclosed that he previously worked in a gold mine for 18 years. Patient was subsequently discharged with plans for urology follow up to undergo TURP.
Discussion: There is a broad range of occupations associated with crystalline silica inhalational exposure. Radiographic imaging of chronic simple silicosis is characterized by multiple pulmonary nodules, typically less than 1 cm in diameter. Complicated cases of silicosis such as progressive massive fibrosis (PMF) may show coalescing pulmonary nodules with associated hilar lymphadenopathy and can mimic malignancy. IARC classified silica as a carcinogen in 1997, and there remains consistent evidence of a causal relationship between silicosis and lung cancer. However, to our knowledge, no correlation between silicosis and prostate cancer has been reported. Our patient presented with sclerotic bony lesions in setting of an enlarged prostate with bilateral pulmonary nodules concerning for metastatic prostate cancer. Though rare, pulmonary metastases from primary prostate malignancy do occur. In a population-based analysis, thoracic metastases accounted for 9.1% of patients with metastatic prostate cancer. The patient in this case had a relatively low PSA level, which argued against advanced prostate cancer. However, progression of disease can occur with low or undetectable PSA levels, with most cases demonstrating poorly differentiated histology. As a result, our patient completed a full work up to exclude this possibility. Ultimately, the diagnosis was biopsy-proven silicosis in the form of PMF.
Conclusions: This case highlights the radiographic similarity between silicosis and metastatic disease, which would have remained a diagnostic challenge without the aid of cytopathological analysis.
