Hyperthyroidism. Autoimmune thyroid disease of the hypermetabolic type (Graves disease) is reflected by several visible changes. The skin is soft and moist. Scalp hair is thin in diameter, and evidence of diffuse alopecia may be present. Vitiligo occurs in 5% to 10%, and alopecia areata occurs in 1 % or 2% of the patients. Onycholysis of the fingernails is sometimes seen. Late in the course of the disease a few patients develop a peculiar form of clubbing (thyroid acropachy) or pretibial myxedema. The latter consists of thickened, pebbly, skin-colored plaques over the lower anterior shins. These plaques are usually asymptomatic.

Diabetes Mellitus

Patients with diabetes mellitus may develop a number of cutaneous changes. The yellow plaques of necrobiosis lipoidica diabeticorum most often located on the anterior shins, are the most distinctive of these changes.Small, hypopigmented, slightly depressed scars (diabetic dermopathy) are also occasionally found on the anterior lower legs. These lesions probably represent obliterative small vessel disease in an area prone to trauma. Bullous lesions somewhat similar in appearance to those of pemphigoid may arise from otherwise normal-appearing skin around the feet and ankles. The cause of these blisters is unknown. Eruptive xanthomas consisting of small, smooth, pink, dome-shaped papules may appear in a sudden shower of lesions in those whose diabetes is grossly out of control. Staphylococcal bacterial infections and candidal yeast infections are seen with increased frequency in diabetic persons. Diabetes is also associated with a variety of other cutaneous and medical conditions.

Neurofibromatosis

The presence of sharply marginated, light brown patches (cafe-au-lait patches) is often the first clue to the presence of von Recklinghausen's disease . In late childhood or during the teenage years, axillary freckling and cutaneous neurofibromas begin to develop. The latter are soft, smooth-surfaced, peduncuated papules 0.5 to 2 cm in diameter. They vary in number from several to hundreds and are distributed randomly over the trunk and extremities. Patients with the most severe forms of neurofibromatosis may develop large, grotesque, sack-like plexiform neuromas. A small proportion of these latter lesions undergo sarcomatous degeneration.

Tuberous Sclerosis

The earliest sign of tuberous sclerosis is generally the presence of small, faint white, oval patches (ash leaf spots) scattered randomly on the trunk and extremities . These lesions may be present at birth or may develop in early childhood. One or more thickened skin-colored plaques (shagreen plaques) may appear on the lower back in late childhood. Towards puberty, pinhead-sized, smooth, red, dome-shaped papules (adenoma sebaceum) begin to emerge on the central portion of the face. The upper lip is spared. Such lesions are easily mistaken for acne papules. Finally, in adult life, small, firm, skin-colored, subungual or periungual fibromas may be noted.

Peutz-Jeghers Syndrome.

This dominantly inherited condition is characterized by the presence of small brown or blackfreckles that appear in clusters on and around the lips and on the fingertips. These pigmentary changes are accompanied by the development of intestinal polyps. Carcinomatous degeneration of these polyps is not common but does occur.

Osler-Weber-Reudu Syndrome

This dominantly inherited condition, also known as hereditary hemorrhagic telangiectasia, is characterized by the presence of small, dusky red, clustered manlles on the fingertips, lips, and mucosal surfaces. These macules are composed of multiple telangiectatic vessels that blanch on pressure. Lesions similar to these may also .occur in patients with the CRST (calcification, Raynaud's phenomenon, scleroderma, and telangiectasia) variant of scleroderma. Patients with this disease have recurrent episodes of epistaxis and gastrointestinal bleeding. Arteriovenous fistulae are sometimes present in the lungs and liver.