This is a classic example of gout. This 74-year-old man developed a painful nodule over his olecranon bursa. He also had elevated serum uric acid. Tophaceous gout results from abnormalities in purine metabolism, leading to elevated serum uric acid and deposition of monosodium urate crystals. These deposits usually are in the ear, elbows, fingers, and toes. The crystals are painful, but interestingly have little inflammation by histology. Foreign-body giant cells often line the deposits. When stored/fixed in ethanol, as opposed to formalin, the crystals become birefringent under polarized light, as in this case.
Histologic sections of skin show amorphous deposits within the dermis. The large deposits are gray-pink with a fibrillary character, bordered by a thin rim of multinucleated giant cells. Needle-like deposits are also displaced within a fibrous stroma. Little inflammation is present.