Renal disease and uremia may be responsible for purpura, edema, or cutaneous ulcerations. Cutaneous lesions that are highly specific and diagnostic for a specific systemic disorder are considered to be a cutaneous markers of that internal disease. Skin lesions may be a marker of internal disease in two different ways. First, the cutaneous changes may be caused by the same etiologic agent or process.which can be identified by examination and evaluation of the skin. Second, cutaneous lesions may be markers when a strong relationship exists between the presence of the skin and internal diseases, even though the primary pathologic processes may not be identical.
Infectious diseases affecting both the skin and internal organs are very common.
Malignancies of internal organs may have concurrent involvement of the skin or cutaneous metastatic lesions, although the incidence of cutaneous metastasis of internal malignancies appears to be low. Biopsy of the skin may not always give the origin of the tumor, however the pathologic process and general tumor type are usually determined. Autoimmune disease may be multisystemic and involve the skin. Examples include systemic lupus erythematosus, pemphigus erythematosus, and a variety of less well-defined immunologic diseases. Histologic and immunodiagnostic evaluation of the skin can be diagnostic.