Thursday 16 June 2011
Skin manifestations, including rheumatoid nodules, are relatively common in rheumatoid arthritis.
These nodules occur in approximately 20% of patients, usually in the vicinity of joints.
Sited primarily in the subcutaneous tissue, they may involve the deep and even the superficial dermis.
They vary from millimeters to centimeters in size and consist of fibrous white masses in which there are creamy yellow irregular areas of necrobiosis.
Old lesions may have clefts and cystic spaces in these regions.
It is most probable that rheumatoid nodules result from a vasculitic process; however, even in very early lesions such a change may be difficult to demonstrate.
Nodules usually persist for months to years. Rarely, similar lesions occur in systemic lupus erythematosus.
Multiple small nodules may develop on the hands, feet, and ears during methotrexate therapy. This event is known as ‘accelerated rheumatoid nodulosis’.
The term rheumatoid nodulosis has also been used for the presence of subcutaneous rheumatoid nodules with recurrent articular symptoms but no significant synovitis.
The rheumatoid factor is often negative. The distinction of this entity from juxta-articular pseudorheumatoid nodules is problematic.
There are one or more irregular areas of necrobiosis in the subcutis and dermis.
These areas are surrounded by a well-developed palisade of elongated histiocytes, with occasional lymphocytes, neutrophils, mast cells, and foreign body giant cells.
The central necrobiotic focus is usually homogeneous and eosinophilic. There is sometimes obvious fibrin.
In contrast, the areas of necrobiosis in the subcutaneous or deep variant of granuloma annulare are often pale and mucinous with a tendency to basophilia.
Old rheumatoid nodules may show areas of dense fibrosis, clefts, and ‘cystic’ degeneration of the necrobiotic foci.
The dermis and subcutis surrounding the necrobiotic granulomas show a perivascular round cell infiltrate which includes plasma cells. Eosinophils may be present.
Uncommonly, an acute vasculitis is seen in the surrounding vessels and sometimes a necrotic blood vessel associated with nuclear fragments or sparse neutrophils may be seen in the center of areas of necrobiosis.
Occasionally, a superficial nodule may perforate the epidermis.
Fibrin is present in the center of the necrobiotic areas.
Rarely, immunoglobulins and complement have been demonstrated in vessels exhibiting a vasculitis.
It is unusual to find mucin in necrobiotic foci in rheumatoid nodules, and this is the single most useful feature in distinguishing these lesions from the deep variant of granuloma annulare.
In some cases of deep granuloma annulare the changes are very similar to those of rheumatoid nodules; clinical information is most helpful in these instances.
A palissade of elongate histiocytes surrounds a zone of ‘necrobiosis’.
necrobiotic granuloma (collagenolytic granuloma)
- granuloma annulare
- necrobiosis lipoidica
- necrobiotic xanthogranuloma
- rheumatoid nodule