Primary lesions are uncomplicated abnormalities that represent the initial pathologic change. Secondary changes reflect progression of disease.
Diagnosis depends upon identification of the primary lesion. Other features, such as distribution, configuration, and color assist in narrowing the diagnosis. These features along with a focused history and knowledge of key clinical features usually result in a specific diagnosis of dermatologic conditions.
The clinician must recognize, and communicate to the patient, that there are times when it is difficult to narrow the final diagnosis to a single entity.
Emergency physicians are faced with a vast range of dermatologic problems. At any given time, there may be a straightforward case of urticaria or a more serious presentation of toxic epidermal necrolysis (TEN) waiting to be seen. The role of the emergency physician is not to diagnose every dermatologic “zebra” but rather to distinguish the trivial from the serious and to identify those conditions which require immediate intervention.
The history can be broken down to a series of questions including:
When did the lesions first develop and what has been the progression of the rash?
Where did the lesions originate?
How does it feel? Does it itch, hurt, or sting?
What made it better or worse? What treatment was applied?
Was there any prodrome to the lesions? What are the associated symptoms?
What kind of exposures have they had, including occupation (applicable for adolescent population), travel, foods, and contacts?
How is the patient’s general health including allergies? What medications do they take regularly or intermittently?
Is there a family history of any skin-related disorders?
What specifically prompted the patient to seek medical care? What do they think is causing the rash?
Dermatology is a visual specialty and diagnosis relies heavily on careful inspection of the skin. The examination should be performed in a well-lit area. The patient should be appropriately exposed so that the eruption can be visualized in its entirety for distribution and configuration. After evaluation of the eruption at a distance, individual lesions are examined. Palpation of the rash confirms consistency and depth. For purposes of this systematic approach, the most important objective of the physical examination is to characterize the morphology of the primary lesion. A thorough description of a rash should include morphology, color, configuration, and distribution.
Morphology describes the general appearance of a rash and can be described in terms of primary and secondary lesions.1–3 Primary lesions are uncomplicated abnormalities which represent the initial pathologic change. Secondary changes reflect progression of disease such as excoriation, infection, or keratinization. The morphologic expression of a dermatologic condition is the basis on which all diagnoses are founded. In some cases, the appearance is distinctive enough to make a diagnosis at a glance (i.e., the grouped vesicular lesions of herpes simplex). In other cases, the appearance may be modified by scratching, secondary infection, or prior treatment. Most importantly, one must recognize that skin disease may evolve over time.
Macule: Circumscribed, flat discoloration of <1 cm in diameter; examples include ash-leaf spots, flat nevi, and freckles. Macules may constitute the whole or part of a rash or may represent the early phase.
Patch: Flat discoloration that is >1 cm in diameter and circumscribed; examples include vitiligo or tinea versicolor. Patches often have a very fine scale on the surface.
Papule: Circumscribed, superficial, solid elevated lesion <1 cm in diameter; examples include warts, elevated nevi, insect bites, and molluscum contagiosum.
Plaque: A lesion >1 cm in diameter elevated, flat top, superficial lesion; examples include psoriasis and pityriasis rosea.
Vesicle: Fluid-filled lesion <1 cm in diameter; examples include herpes simplex and varicella.
Bulla: Fluid-filled lesion >1 cm in diameter; examples include staphylococcal scalded skin syndrome and bullous impetigo.
Pustule: Pus-filled lesion; examples include acne and folliculitis.
Nodule: Lesion <1 cm in diameter with depth, may be below, above, or at the surface of the skin; examples include fibromas and lesions of erythema nodosum.
Tumor: Solid lesion >1 cm with depth, which may be below, above, or at the surface of the skin; examples include lipomas.
Petechiae: Pinpoint <1 cm flat, round red spots under the skin surface, because of deposits of blood and/or pigment; examples include drug eruption, Rocky Mountain spotted fever.
Purpura: Visible collection of blood/pigment >1 cm in diameter; examples include Henoch–Schönlein purpura and idiopathic thrombocytopenia purpura.
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