General internists, in their day-to-day clinical interactions, will often be called upon to evaluate dermatologic problems. A thorough understanding of the skin and its associated structures is required (Figure 1).
Morphology of skin lesions can be categorized as primary or secondary. Primary skin lesion morphology is the appearance of a rash or growth in its initial or unaltered state. Dermatologic conditions can be categorized as growths or rashes. Growths are localized areas of abnormal skin, whereas rashes are more widespread in appearance. Over time, with itching or rubbing, secondary skin changes may occur.
Table 1 lists primary and secondary skin lesions. Other important characteristics of skin lesions include color, distribution, grouping, and configuration. Rather than focusing initially on identification of specific rashes and their characteristics, a differential diagnosis should be developed based on morphologic features of the primary skin disease. For example, a linear pattern is often seen in contact dermatitis, a grouped pattern is seen in herpes viral infections, and tinea infections are often annular.
No standardized method has been developed for how to best perform a full-body skin examination, but experts agree that patients should be fully undressed and covered with an examination gown. Attempting to perform a full-body skin examination by having patients lift their shirt or roll up their sleeves is insufficient. Proper lighting is essential, as side lighting can often detect subtle elevations of the skin. A systematic approach is recommended. One method is to start with the head and neck, working down to the torso, upper extremities, and lower extremities. Care should be taken to ensure that the digits, umbilicus, and scalp are thoroughly examined. A full-body skin examination should take 2 minutes. The routine skin examination may be incorporated into the complete physical examination by assessing the torso when auscultating the heart and lungs, the arms while checking blood pressure and pulse, and the back while listening to the lungs. The skin examination is a good time to reinforce ultraviolet light protection techniques and review the signs and symptoms of skin cancer (see Common Neoplasms). The most recent U.S. Preventive Services Task Force (USPSTF) statement found insufficient evidence to screen adults for skin cancer, including persons with increased risk of skin cancer.
Rashes in persons with skin of color may be harder to detect since the pink-red color that is a sign of inflammation can be more subtle on darker skin. Persons with skin of color often have normal variations in skin color with areas of hyperpigmentation along the gingiva and lines of demarcation on the trunk and extremities. Scrapes, bug bites, or acne often heal with hyperpigmentation. Areas of active inflammation from seborrhea, eczema, or psoriasis may develop hyper- or hypopigmentation.
Diagnostic tools and tests that may augment the physical examination include preparation of specimens using potassium hydroxide (KOH), wet mounting, or Tzanck preparations; and use of a Wood lamp or a dermatoscope to visualize lesions. These techniques and tools are easy to use and have minimal equipment requirements; however, skill and experience are necessary for accurate and reliable interpretation.
If tinea or candida is suspected, a scraping of the skin at the leading edge of the rash is done. The scale is placed on a microscope slide, and KOH is applied to the specimen. The presence of branching hyphae indicates tinea, whereas the presence of pseudohyphae indicates candida. Similarly, a wet mount is done when evaluating for scabies. In this case, mineral oil is used in place of KOH. Mineral oil will allow the scabies mite to stay alive and will aid in detection.
A Wood lamp is an inexpensive ultraviolet light that can be used to evaluate hypo- and depigmentation as seen in vitiligo. It can also detect skin fluorescence associated with erythrasma and the urine fluorescence in patients with porphyria cutanea tarda. The Tzanck preparation can detect multinucleated giant cells within a blister cavity, thus determining a herpes viral infection. The Tzanck preparation does not distinguish between members of the herpes virus family. A hand-held microscope, called a dermatoscope, is a tool used predominately to help with the evaluation of pigmented skin lesions.
In addition, no office is complete without a camera and the capability to store photographs. Serial photographs can be used to follow the progress or improvement of a rash, to follow changes in a pigmented nevus, or to document the location of biopsy sites for proper location.
The clinician must determine whether a patient has a dermatologic emergency or urgency that requires immediate intervention or referral. Table 2 describes situations that mandate immediate intervention or referral to a specialist.