30/04/2023
Pseudoxanthomatous rheumatoid nodule. Taro Horino, MD Satoshi Inotani, MD Hideki Nakajima, MD
Hiroshi Ohnishi, MD Masahiro Komori, MD Osamu Ichii, PhD et al. The Lancet Rheumatology. VOLUME 5,
ISSUE 2, E110, FEBRUARY 2023
A 69-year-old woman with a 27-year history of rheumatoid arthritis presented to the rheumatology
clinic at Kochi Medical School hospital, Japan, with polyarthralgia of both hands and painless
subcutaneous nodules on her right hand that had slowly grown over a year. Physical examination
revealed arthritis mutilans with ulnar deviation and yellow masses on the metacarpophalangeal joints of
the fingers of the right hand (figure A). There were no abnormal findings in any part of the body other
than the joints, such as the eyelids and trunk. Laboratory investigations revealed that the levels of C-
reactive protein (CRP) and rheumatoid factor were 1·78 mg/dL (normal range <0·15 mg/dL) and 1 096·0
IU/mL (<15 IU/mL), respectively. Hyperlipidaemia, cryoglobulinemia, hypocomplementemia, and
monoclonal paraproteins were not detected. We performed a bone marrow biopsy, which was
normocellular. An x-ray revealed severe erosion and deformities of the hand bones and punched-out
bony radiolucencies associated with the subcutaneous nodular lesions (figure B). A skin biopsy specimen
of the subcutaneous mass showed areas of cholesterol clefts and necrobiosis surrounded by foamy
histiocytes, lymphocytes, Touton giant cells, and foreign body-type multinucleated giant cells (figure
C–F). These findings confirmed a diagnosis of pseudoxanthomatous rheumatoid nodule.
Pseudoxanthomatous rheumatoid nodules are an unusual form of rheumatoid nodule resembling
tendon xanthomas, are often mistakenly diagnosed as xanthomatosis, and have been previously
regarded by investigators as subcutaneous xanthogranuloma, observed in the juxta-articular sites of the
hand, wrist, elbow, knee, foot, and acromioclavicular joints. Pseudoxanthomatous rheumatoid nodules
are distinguished from xanthomatosis by x-ray findings of demonstrable punched-out bony
radiolucencies, which are not present in xanthomatosis. Cholesterol clefts surrounded by granulomatous
reactions can also be observed in rheumatoid synovial fluid and bursitis, sometimes presenting as
migrating chylous cysts. Pseudoxanthomatous rheumatoid nodule and xanthomatosis are easily
misdiagnosed because their histopathological findings are similar. However, xanthomatosis is often
associated with hyperlipidaemia, cryoglobulinemia, hypocomplementemia, and monoclonal
paraproteins, whereas pseudoxanthomatous rheumatoid nodule is not accompanied by these diseases
and is found in the juxta-articular sites with punched-out bony radiolucencies. After initiating treatment
with 6 mg oral methotrexate per week, the concentrations of CRP reduced to 0·63 mg/dL, polyarthralgia
improved, and the pseudoxanthomatous rheumatoid nodules shrank.