Aspiration cytopathology of tophaceous gout: a report of 22 patients

Abstract

Gout may manifest with crystal-induced arthropathy and/or soft tissue tophi. Demonstration of monosodium urate (MSU) crystals is necessary to establish the diagnosis. Despite the fact that alcohol is an ideal fixative to preserve MSU crystals, very few fine-needle aspiration (FNA) cases of gout have been published. A retrospective review was performed for FNA cases diagnosed as tophaceous gout. Samples included unstained smears or smears stained with Diff-Quik or Papanicolaou stain, and formalin-fixed paraffin-embedded cell block stained with hematoxylin and eosin (H&E). We identified 22 FNA cases involving 18 men and 4 women. Only 7 patients had a clinical history of gout and 5 were taking gout medication. At least 4 patients presented with a clinical diagnosis of rule out sarcoma. All had soft tissue masses from either upper (n = 5) or lower (n = 17) extremities. Extracellular polarizing needle-shaped crystals with negative birefringence were present and visible on unstained, Diff-Quik, or Papanicolaou-stained conventional smears as well as in H&E-stained cell blocks in all cases. Our study demonstrates that MSU crystals are readily detectable under polarization on direct smears with or without staining. FNA cytology can serve as an alternative to core needle biopsy or synovial biopsy in not only confirming a diagnosis of tophaceous gout, but also in eliminating a diagnosis of soft tissue sarcoma in those patients where clinical and/or radiologic features were concerning for malignancy.