Patients with connective tissue diseases, particularly scleroderma, show periungual erythema and nailfold capillary abnormalities. Periungual erythema and nailfold capillary abnormalities, which were studied by means of capillary microscopy and canonical discriminant analysis, were compared. The rate of occurrence of abnormal capillary patterns in scleroderma, systemic lupus erythematosus, primary Sjögren’s syndrome, primary and secondary Raynaud’s phenomenon, and diabetes mellitus was significantly higher than that in normal controls. All patients with mixed connective tissue disease and dermatomyositis/polymyositis showed abnormal capillary patterns. The incidence of periungual erythema in those cases of scleroderma, primary and secondary Raynaud’s phenomenon, and diabetes mellitus showing abnormal capillary patterns was significantly higher than those showing a normal capillary pattern. Periungual erythema in mixed connective tissue disease and dermatomyositis/polymyositis was associated with an abnormal capillary pattern. The observation of periungual
erythema is a simple and useful way of detecting connective tissue diseases in clinical practice.