Woman, 32, With Crusty Red Blisters

DIFFERENTIAL DIAGNOSIS
Because multiple bacterial and viral diseases manifest in this fashion, the differential diagnosis included the following ­disorders:

Erythema multiforme. This skin condition may result from an allergic or hypersensitivity reaction to certain drugs or from infections. Infections that can cause erythema multiforme include herpes simplex virus and mycoplasma. Patients present with lesions on the palms (see Figure 3), soles, extremities, face, or trunk. The lesions can appear as a nodule, papule, macule, or vesicle. Initially, in the mild form, the lesions may appear as hives or target-shaped rashes, occurring on the face and acral surfaces. A severe form of erythema multiforme, known as Stevens-Johnson syndrome, is characterized by rash, mucosal involvement, and systemic symptoms.¹

Herpes zoster. This viral infection is caused by the varicella-zoster virus, which also causes chicken pox. The virus lies dormant within a single sensory ganglion and may reappear as shingles along the dermatome of that nerve. Patients may experience burning or shooting pain with tingling or itching before the rash appears; vesicular lesions with erythematous bases appear days later. The rash occurs unilaterally on the body or face and does not cross the midline. A viral culture may be obtained for identification.²

Herpetic gingivostomatitis. This infection is most commonly caused by herpes simplex virus type 1, the same virus that causes cold sores. Patients may present with ulcerations along the buccal mucosa and gums. The infection manifests with systemic symptoms, including malaise, fever, irritability, and cervical adenopathy. A viral culture will identify the etiology.³

Impetigo. This skin infection is typically caused by bacteria, predominantly Staphylococcus aureus, Streptococcus pyogenes, or a combination. Infections generally occur after a break in the skin surface. The most common presentation is a rash that spreads to different parts of the body after scratching. Skin lesions can occur on the face, lips, or extremities. Initially vesicular, the lesions generally form a honey-colored crust after fluid discharge. The clinician should take a skin or fluid sample from the lesion to culture, which may identify the pathogen.⁴

Syphilis. This sexually transmitted infection is caused by the spirochete Treponema pallidum. In primary syphilis, patients can develop a painless sore, or chancre, on the genitals, rectal area, or mouth. If left untreated, the disease can progress to secondary syphilis, manifesting as a pale pink or reddish maculopapular rash on the palms and soles. The rash can be associated with fever, sore throat, myalgia, and fatigue. It is important to rule out syphilis because, left untreated, it can lead to cardiac and neurologic complications. Screening tests include VDRL and the rapid plasma reagin (RPR) test, both of which assess for antibodies to the organism, and dark field microscopy of ulcerations to identify the organism.⁵

Also included in the differential diagnosis for the patient’s symptoms was hand-foot-mouth disease (HFMD), discussed below.

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