Rheumatoid Nodule: Subcutaneous nodules seen in 20-30% of rheumatoid arthritis patients. They may arise anywhere on the body, but are most frequently found over the bony prominences. The nodules are characterized histologically by dense areas of fibrinoid necrosis with basophilic streaks and granules, surrounded by a palisade of cells, mainly fibroblasts and histiocytes.Rheumatic Nodule: A small round or oval, mostly subcutaneous nodule made up chiefly of a mass of Aschoff bodies and seen in cases of rheumatic fever. It is differentiated from the RHEUMATOID NODULE which appears in rheumatoid arthritis, most frequently over bony prominences. (From Dorland, 27th ed)Neuroma: A tumor made up of nerve cells and nerve fibers. (Dorland, 27th ed)Arthritis, Rheumatoid: A chronic systemic disease, primarily of the joints, marked by inflammatory changes in the synovial membranes and articular structures, widespread fibrinoid degeneration of the collagen fibers in mesenchymal tissues, and by atrophy and rarefaction of bony structures. Etiology is unknown, but autoimmune mechanisms have been implicated.Chimerism: The occurrence in an individual of two or more cell populations of different chromosomal constitutions, derived from different individuals. This contrasts with MOSAICISM in which the different cell populations are derived from a single individual.Rheumatoid Factor: Antibodies found in adult RHEUMATOID ARTHRITIS patients that are directed against GAMMA-CHAIN IMMUNOGLOBULINS.Leprosy, Lepromatous: A chronic communicable infection which is a principal or polar form of LEPROSY. This disorder is caused by MYCOBACTERIUM LEPRAE and produces diffuse granulomatous skin lesions in the form of nodules, macules, or papules. The peripheral nerves are involved symmetrically and neural sequelae occur in the advanced stage.Elbow: Region of the body immediately surrounding and including the ELBOW JOINT.