A 48-year-old African-American man with a history of diabetes and hypertension presents to your clinic complaining of a rash on his leg. It has been present for several months and is progressively getting worse. His diabetes is poorly controlled; diabetic complications include both chronic renal insufficiency and retinopathy. On physical examination, you note an 8 cm atrophic patch with a yellow central area and enlarging erythematous borders. This patient's symptoms are most consistent with which of the following cutaneous manifestations of diabetes?

A. Acanthosis nigricans
B. Necrobiosis lipoidica
C. Scleroderma
D. Erythrasma

(Answer: B—Necrobiosis lipoidica)

Key Concept/Objective: To recognize necrobiosis lipoidica as a potential skin manifestation of diabetes

Necrobiosis lipoidica is a specific cutaneous manifestation of diabetes. Lesions consist of chronic atrophic patches with enlarging erythematous borders. The legs are most commonly affected. The center of lesions appears yellow because of subcutaneous fat that is visible through the atrophic dermis and epidermis. Occasionally, the lesions ulcerate. Necrobiosis lipoidica is often associated with diabetic nephropathy or retinopathy. Acanthosis nigricans has been reported in patients with insulin resistance syndrome; however, the lesions are velvety to the touch, are black in color, and are located predominantly in contact areas such as the axilla. Scleroderma causes subcutaneous infiltration of the skin, mostly in the trunk of patients with long-standing diabetes. Erythrasma is a fungal infection affecting the fifth intertriginous space.�

A 24-year-old man comes to your office with complaints of a diffuse, mildly pruritic rash that developed over the past 1 to 2 weeks. Examination reveals a papular eruption involving the trunk and extremities. You suspect pityriasis rosea. Which of the following statements regarding the clinical features of pityriasis rosea is false?

A. Lesions typically occur on the trunk in a symmetrical fashion and form cleavage planes on the skin
B. The development of a herald-patch lesion 7 to 10 days before the onset
of the diffuse eruption helps establish the diagnosis
C. Pityriasis rosea typically involves the palms and soles
D. The disorder is usually self-limited

(Answer: C—Pityriasis rosea typically involves the palms and soles)

Key Concept/Objective: To understand the distinguishing features of pityriasis rosea�

Pityriasis rosea is a self-limited, exanthematous disease that manifests as oval papulosquamous lesions typically distributed in a symmetrical fashion over the trunk and extremities. The exact etiology is unclear, but viral triggers have been suggested. The eruption is usually preceded by a primary lesion consisting of a slightly raised, salmon-colored oval patch with fine scaling (the “herald patch”). Lesions tend to follow lines of cleavage on the skin and may appear on the back in a typical “fir tree” or “Christmas tree” distribution. The differential diagnosis of pityriasis rosea lesions includes secondary syphilis, tinea corporis, and tinea versicolor. The appearance of lesions on the palms and soles is more typical of secondary syphilis and may help distinguish this rash from pityriasis rosea. If there is high suspicion of syphilis or if the diagnosis is unclear, a serologic test for syphilis is warranted. The lesions of pityriasis rosea typically resolve spontaneously in 6 to 8 weeks.

For an otherwise healthy individual with typical pityriasis rosea, which of the following would NOT be an appropriate option for treating symptoms?

A. Low-potency topical steroids for lesions on the trunk
B. Oral antihistamines
C. Oral erythromycin
D. Use of ultraviolet B (UVB) or exposure to sunlight early in the course of the eruption
E. Retinoic acid

(Answer:E—Retinoic acid)

Key Concept/Objective: To understand the treatment options for pityriasis rosea

Pityriasis rosea is typically self-limited, but several treatment options exist. Foremost, patients should be reassured and educated about the benign nature of the disease. If pruritis is a prominent symptom, oral antihistamines are usually effective. Low-potency topical steroids have been shown to be of benefit. Exposure to ultraviolet light has been shown to shorten the duration of the eruption, especially if treatment is started within the first week of onset. A single trial demonstrated that a 14-day course of oral erythromycin was safe and led to complete resolution of the eruption within 2 weeks in a third of patients. Retinoic acid has not commonly been employed to treat pityriasis rosea.�

A 35-year-old woman presents to clinic complaining of a pruritic rash on her hands. She denies recently changing the detergents and soaps she uses, and she does not wear jewelry. She admits to being under a great deal of stress at work over the past few days. Examination is notable for small, clear vesicles on the sides of her fingers, and there is associated evidence of excoriation. What is the most likely diagnosis for this patient?

A. Nummular eczema
B. Contact dermatitis
C. Dyshidrotic eczema (pompholyx)
D. Seborrheic dermatitis

(Answer: C—Dyshidrotic eczema [pompholyx])

Key Concept/Objective: To know the differential diagnosis of eczematous disorders and to recognize the presentation of dyshidrotic eczema

Eczema is a skin disease characterized by erythematous, vesicular, weeping, and crusting patches associated with pruritus. The term is also commonly used to describe atopic dermatitis. Examples of eczematous disorders include contact dermatitis, seborrheic dermatitis, nummular eczema, and dyshidrotic eczema (pompholyx). Contact dermatitis is very common and can be induced by allergic or irritant triggers. The distribution of the rash in contact dermatitis coincides with the specific areas of skin that were exposed to the irritant (e.g., in patients sensitive to nickel, rashes may appear on fingers on which rings containing nickel are worn; in patients sensitive to detergent, rashes may appear on areas covered by clothing containing detergent). This patient does not have a history of any particular exposure, and the rash occurs only on the sides of several fingers. Seborrheic dermatitis is also common and is characterized by involvement of the scalp, eyebrows, mustache area, nasolabial folds, and upper chest. Nummular eczema is characterized by coinshaped patches occurring in well-demarcated areas of involvement. This patient most likely suffers from dyshidrotic eczema, which tends to occur on the side of the fingers, is intensely pruritic, and often flares during times of stress. The treatment includes compresses, soaks, antipruritics, and topical steroids. Severe cases may require systemic steroids.�

A 21-year-old man presents to the acute care clinic complaining of itching. He states that since childhood, he has had a recurrent rash characterized by “red, itchy, dry patches” of skin. Sometimes the rash is associated with “little bumps.” Examination of his skin reveals erythematous, scaling plaques on the flexural surfaces of his arms with associated excoriations. You suspect the patient has atopic dermatitis. Of the following findings, which is NOT among the major diagnostic criteria of atopic dermatitis?

A. Personal or family history of atopy
B. Pruritus
C. Chronic or chronically recurring dermatosis
D. Elevated serum IgE level

(Answer: D—Elevated serum IgE level)

Key Concept/Objective: To recognize the clinical presentation of atopic dermatitis and to know the major diagnostic criteria�

Atopic dermatitis is a clinical diagnosis. The major diagnostic criteria for atopic dermatitis include a personal or family history of atopy (including asthma, allergic rhinitis, allergic conjunctivitis, and allergic blepharitis); characteristic morphology and distribution of lesions (usually eczematous patches in flexural areas in adults and extensor surfaces in hildren who crawl; lichenification can occur with nodule formation in chronic cases); pruritus (virtually always present); and a chronic or chronically recurring course. An elevated serum IgE level is not a major diagnostic criterion. This patient is somewhat unusual in that his childhood atopic dermatitis has persisted past puberty (this occurs in only 10% to 15% of cases).�

An 18-year-old woman presents for treatment of chronic dry skin and scaling. The rash typically involves the extensor surfaces of her extremities. She notes that she has had this condition since infancy and that her father has it as well. Her medical records indicate that she has been diagnosed with ichthyosis vulgaris by a dermatologist. Which of the following statements is false?

A. The ichthyoses are a group of diseases characterized by abnormal cornification of the skin leading to excessive scaling�
B. Ichthyosis can be an acquired condition associated with endocrinopathies, autoimmune diseases, HIV infection, lymphomas, and carcinomas
C. The most common form of ichthyosis is acquired ichthyosis
D. Treatment of ichthyosis includes emollients and keratolytics

(Answer: C—The most common form of ichthyosis is acquired ichthyosis)

Key Concept/Objective: To know the presentation of ichthyosis vulgaris and to be familiar with the ichthyoses

Etiologies of the ichthyoses are diverse, but the ichthyoses share common manifestations and treatments. The most common form is ichthyosis vulgaris, which is inherited in an autosomal dominant fashion (as seen in this patient); disease onset occurs in patients 3 to 12 months of age. Other forms of ichthyoses include recessive X-linked ichthyosis, lamellar ichthyosis, congenital ichthyosiform erythroderma, epidermolytic hyperkeratosis, and acquired ichthyosis. Acquired ichthyosis is associated with multiple disorders, including HIV infection and endocrinopathies; it can also occur as a paraneoplastic syndrome that is usually associated with lymphomas and carcinomas. Epidermolytic hyperkeratosis is the most difficult form to treat because therapeutic agents can induce blistering. Standard therapies are emollients (such as petrolatum) and keratolytics (such as lactic acid with or without propylene glycol). Antimicrobial agents are also frequently used to combat the odor and other complications of bacterial colonization of the affected skin.�

A 30-year-old salesman in a party supply store that specializes in balloons develops a severe pruritic erythematous diffuse skin reaction after eating avocado. What is the most likely explanation for this patient’s reaction?

A. Delayed type IV reactivity to the avocado as the primary allergen
B. Immediate type I reactivity to the avocado as the primary allergen
C. Irritant contact dermatitis reaction to the avocado
D. Immediate type I cross-reactivity reaction to the avocado with primary latex allergy as the underlying allergic cause
E. IgM-mediated allergic reaction

Answer: D— Immediate type I cross-reactivity reaction to the avocado with primary latex allergy as the underlying allergic cause

Key Concept/Objective: To understand natural rubber and latex allergy and cross-reactivity with certain fruits, including avocados, chestnuts, kiwi, and bananas

The patient has a history of exposure to latex through his work with balloons, and he develops a systemic pruritic reaction after eating avocado. The immediate reaction time rules out a type IV reaction, which usually takes 12 to 48 hours to occur. This patient would not be having an irritant reaction, because his exposure reaction is diffuse, not focal, as would be the case with irritant contact dermatitis. The latex allergic reaction is mediated through IgE, not IgM.�

What is the best method of distinguishing irritant contact dermatitis from allergic contact dermatitis?

A. History of exposure frequency
B. Examination of clinical features and distribution of rash
C. Patch testing
D. Histologic evaluation of skin biopsy of rash
E. Family and travel history

(Answer: C—Patch testing)

Key Concept/Objective: To understand the value of patch testing in distinguishing irritant contact dermatitis from allergic contact dermatitis

Determining the etiology of a contact dermatitis is difficult. The gold standard is patch testing, although its sensitivity and specificity vary with the tested allergen. Although history of exposure and examination of the distribution and quality of the reaction are valuable, the best method of distinguishing a contact irritant reaction from an allergic contact reaction is patch testing. The histologies of contact irritant dermatitis and allergic dermatitis are identical, and therefore, histologic evaluation would not be useful in determining whether a reaction is allergy-related.�

A 19-year-old female college student is taking ampicillin and clavulanate for pharyngitis. After 5 days of treatment, she develops a generalized erythematous maculopapular rash. She is given a monospot test, and the result is positive. For this patient, which of the following statements is true?

A. Exanthematous rashes may occur in up to 80% of patients with infectious mononucleosis that is treated with ampicillin
B. The patient should undergo skin testing with penicilloyl polylysine and graded desensitization before any treatment with penicillins
C. Treatment should include changing to a macrolide antibiotic
D. The patient is experiencing a type II, or cytotoxic, hypersensitivity reaction
E. The rash will worsen until ampicillin is stopped

(Answer: A—Exanthematous rashes may occur in up to 80% of patients with infectious mononucleosis that is treated with ampicillin)

Key Concept/Objective: To be able to recognize typical ampicillin rash

The causal mechanism of an exanthematous ampicillin rash in the setting of a concurrent viral illness is unclear. It does not appear to be mediated by IgE, so b-lactams can be tolerated and sensitivity testing is not warranted. Although stopping ampicillin is suggested, the rash will generally resolve even if ampicillin is continued.�

In contrast to exanthematous rashes, which of the following is true of urticaria that develops after drug exposure?

A. Type I immediate hyersensitivity reactions cause all urticarial rashes
B. In severe reactions with angioedema and bronchospasm, plasmapheresis should be initiated early in treatment
C. Urticarial rashes remain fixed for up to several days and may recur in the same location with repeated exposure to the causative drug
D. Because of the risk of severe reactions, patients with drug-induced urticaria should not undergo skin testing or desensitization
E. Biopsy should be considered for urticarial lesions that persist for longer than 24 hours

(Answer: E—Biopsy should be considered for urticarial lesions that persist for longer than 24 hours)

Key Concept/Objective: To know the complications associated with urticarial rashes

For lesions that persist for longer than 24 hours, consideration should be given to the use of biopsy to exclude vasculitis. Biopsy may show deposits of IgM and C3 immune complexes within the lesions. Besides being associated with type I reactions, urticaria may occur with type III hypersensitivity reactions and as a result of nonimmunologic release of histamine caused by certain drugs, such as morphine. Treatment of severe allergic reactions includes epinephrine, antihistamines, bronchodilators, corticosteroids, and supportive reatment with fluids and pressors if needed. Patients can be desensitized if there is no therapeutic alternative to the causative drug.