Two cases of patients with an unusual form of rheumatoid nodules closely resembling tendon xanthomas are reported. The disease process was mistakenly diagnosed by numerous physicians as xanthomatosis in one case and as gouty tophi in the second case.
The differential diagnosis of rheumatoid nodules rests on clinical and laboratory findings plus histologic confirmation. Occasionally, the onset of nodule formation antedates the onset of arthritis, adding to diagnostic confusion. This is to be distinguished from the entity, pseudorheumatoid nodules, which has been proposed to explain those rare cases where clinically and pathologically typical nodules persist over many years without the development of associated signs of rheumatoid arthritis.
The development of x-ray demonstrable "punched out" bony radiolucencies in association with subcutaneous rheumatoid nodules is stressed.
Watt TL, Baumann RR. Pseudoxanthomatous Rheumatoid Nodules. Arch Dermatol. 1967;95(2):156-160. doi:10.1001/archderm.1967.01600320012002