The nail apparatus in collagen disorders.

Patients with collagen disorders may have a broad spectrum of nail changes. This article reviews the modifications of the nail apparatus that can be observed in the following diseases: systemic sclerosis, systemic lupus erythematosus, dermatomyositis, mixed connective tissue disease, rheumatoid arthritis, periarteritis nodosa, and Wegener granulomatosis. In all collagen diseases, the proximal nail fold is the most important site of alterations, and a careful inspection of this nail constituent is an essential part of the patient's routine clinical evaluation. Erythema and telangiectasia associated with visualization of the capillary loops are frequent findings; nail fold capillary hemorrhages and focal necrosis are also observed. The nail fold capillary microscopy abnormalities and the special nail changes that can be observed and characterize each collagen disorder are described. A careful clinical examination of the nail and a capillary microscopy study of the prossimal nail fold may, therefore, be decisive for the diagnosis of the collagen disorders. In fact, the nail unit alterations may give a clue that should not be overlooked.