The skin is immunologically and metabolically dynamic, highly vascular, and directly interfaces with the environment. It also plays a critical role in maintenance of homeostasis, protection, and sensation. As such, cutaneous pathology is a window to many systemic disease processes. A careful history and thorough physical examination of the skin, hair, nails, and mucosal surfaces, paying particular attention to morphology, distribution, and other subtle clinical clues, may result in critical diagnostic, prognostic, and therapeutic benefit that is acquired at the bedside. For example, recognition of nailfold capillary abnormalities may distinguish the hand rash seen in dermatomyositis from that observed in eczema and lead to a diagnosis of interstitial lung disease, or underlying hepatitis C viral infection may be uncovered through identification of oral erosive lichen planus.
The following sections will discuss important skin signs in systemic diseases, with particular focus on autoimmune connective tissue disorders and diseases of the endocrine, gastrointestinal, hepatic, pulmonary, and renal organ systems.
AUTOIMMUNE CONNECTIVE TISSUE DISORDERS
Autoimmune connective tissue disorders are a heterogeneous group of immunologically complex diseases. Diagnosis may be challenging because manifestations are often protean and overlap conditions are frequent. The clinical presentation ranges from mild and skin-limited to severe, life-threatening multisystem disease, and patients may require broad-spectrum systemic immunosuppressants to adequately control symptoms and progression. Due to their diverse symptomatology, a multi-disciplinary approach may often provide the best care for patients. In the following sections, lupus erythematosus, dermatomyositis, systemic sclerosis, and vasculitis will be discussed. Important cutaneous manifestations of other autoimmune connective tissue disorders will also be briefly reviewed.
Lupus erythematosus (LE) is a complex autoimmune disorder that affects multiple organ systems and has a wide variety of clinical and immunologic manifestations. Cutaneous involvement is particularly common and may lead to substantial morbidity or disfigurement, profound impact on quality of life, and serve as a marker for underlying systemic disease. We will focus this discussion on lupus-specific phenotypes including acute cutaneous lupus erythematosus (ACLE), subacute cutaneous lupus erythematosus (SCLE), and discoid lupus erythematosus (DLE); the most common form of chronic cutaneous lupus erythematosus (CCLE). A brief discussion of several less common lupus-specific presentations and lupus-nonspecific cutaneous disease will follow. It is common for patients to demonstrate multiple cutaneous phenotypes, particularly if there is underlying systemic lupus erythematosus (SLE).
In North America, SLE has a prevalence of about 240 per 100,000 people.1 Cutaneous lupus erythematosus is at least as prevalent as the systemic variant according to population-based studies.2,3 Risk is highly dependent on demographic factors, most prominently sex and ethnicity, though there is variation between different phenotypes. Overall women are affected at 5–6 times the rate of men, and African Americans are more likely to have LE, and more severe disease, than White or ...