[Needle biopsy in gout and pseudogout (author's transl)]

Radiological and morphological findings in advanced arthritis urica and pyrophosphate arthropathy are well known. In contrast, the early changes of synovial membrane in these disturbances of metabolism pose diagnostic problems. With the assistance of various cytological techniques and polarizing microscopical as well as electron microscopical investigation it was examined to what extent needle biopsies can be helpful in the differential diagnosis of gout and pseudogout.

In 8 patients with gout and 11 patients with pseudogout synovial fluid and small tissue specimens could be obtained with the aid of the Parker-Pearson needle. Both fluid and tissue specimens were investigated light and electron microscopically. Cell counts were evaluated in a Rosenthal chamber. The differentiation of the cells in stained smears was done by counting 200-600 cells per case. Crystals were identified by polarizing microscopy in wet preparations of freshly aspirated synovial fluid.

Polarizing microscopy of synovial fluid detected intra- as well as extracellular urate and pyrophosphate crystals. The wedge-shaped urate crystals and the larger partly polygonal pyrophosphate crystals showed different polarizing microscopical properties and a negative birefringence. The absolute cell counts in gout were higher than those in pseudogout. The relative cell counts of the different cell types in synovial fluid showed more variation in gout than in pseudogout. Cases with acute gout developed a relative leukocytosis in contrast to a relative lymphocytosis in chronic gout. A relative leukocytosis was constant in all patients with pseudogout. Sclerosed areas with scarce and plump villi as well as sometimes hyperplastic and polymorphous synovial cell layers could be demonstrated histologically in the tissue specimens of the needle biopsies in cases with gout. Urate crystals were less frequent in specimens fixed in formalin. The histological alterations in pseudogout were uniform, 2-4 rows of slightly pleomorphic synovial cells lined the inner surface of the joint capsule, sclerosing alterations were less frequent. Pyrophosphate crystals and calcified particles were seen within the synovial lining cells, the connective tissue and the enodthelial cells of the blood vessels in pseudogout specimens. Intra- as well as extracellular crystals could also be demonstrated with the aid of scanning electron microscopy in sediments of synovial fluid in gout and pseudogout. Transmission electron microscopical investigations of synovial tissue specimens detected proliferated and pleomorphic synovial lining cells in gout in contrast to a more monomorphic appearance of these cells in pseudogout. The crystals were washed out during the preparation techniques for transmission electron microscopy so that needle-like empty spaces resulted within cytoplasm of the phagocytic cells. These clefts were surrounded by phagosomal structures and densified cytoplasmic ground substance; sometimes they were also lined by membranes...