Is a dog to blame for these itchy lesions?

Case 1:
For several months, a 28-year-old man has had these changes to his nails, which have also become more brittle. He denies any history of trauma to the nails. When asked if he has any rashes, he lifts his pant leg, as shown here. What do you suspect?

A. Lichen planus.
B. Psoriasis.
C. Trauma.
D. Iron deficiency.
E. Beau lines.

Case 1: Lichen planus

Biopsy of a lesion on the patient’s shin confirmed the diagnosis of lichen planus, A. This condition is associated with nail changes in up to 10% of affected patients. Among the changes seen with lichen planus are roughtextured nails with longitudinal ridging. Corticosteroids— either topical with occlusion or administered by injection—may help resolve these nail changes.

Psoriasis is usually characterized by nail pitting and separation of the nail plate from the nail bed. Beau lines are transverse lines in the nail plate that result from trauma to the cuticle; this patient had no history of trauma. Iron deficiency anemia typically produces spoon-shaped, or concave, nails.

Case 2:
After 6 weeks of coping with itchy lesions on her arms and legs, a 43-year-old woman seeks medical advice. The rash first erupted with the onset of cold weather. The patient recently acquired a dog.

Which of the following questions do you ask?

A. What are your bathing habits?
B. What soap do you use?
C. Do you apply moisturizer?
D. Do other family members complain of itching?
E. Do you have a history of seasonal allergies?

Your differential diagnosis includes which of the following?
F. Psoriasis.
G. Dermatophyte infection.
H. Nummular eczema.
I. Contact dermatitis.
J. Pityriasis rosea.

Case 2: Nummular eczema

This patient with atopy and a history of seasonal allergies, E, bathed with scented soap, B; used a washcloth, A; and failed to apply moisturizer, C, consistently. Nummular eczema, H, resulted. She was the only family member to complain of itching, D.

It is unlikely that a dermatophyte infection would produce multiple lesions; typically only 1 or 2 highly inflamed lesions occur when a dog or a cat is the source of ringworm. If in doubt, perform a potassium hydroxide evaluation to rule out a dermatophyte.

Contact dermatitis arises on exposed areas of the body; because of the cold weather, the patient’s arms and legs had been covered. Pityriasis rosea occurs on the trunk and psoriasis affects the knees and elbows, which were clear in this patient.

Case 3:
During a routine examination, these changes are noted on both thumbnails of a 56-year-old man. He denies any trauma or underlying diseases. What does this look like to you?

A. Trauma.
B. Lichen planus.
C. Psoriasis.
D. Iron deficiency.
E. Beau lines.

Case 3: Median nail dystrophy

Further questioning revealed that the patient had a compulsive habit of picking at his cuticle. Median nail dystrophy secondary to trauma, A, was diagnosed. None of the other conditions in the differential are associated with median nail dystrophy. If the condition has not persisted too long and the picking has not scarred the nail matrix, the nails will grow out normally in some patients.

Case 4:
For 3 weeks, a 28-year-old man has had a pruritic, bilateral axillary rash. He stopped using deodorant, but the condition has not improved. The patient takes no medication and is otherwise healthy, although he reports having had a mild upper respiratory tract disorder that did not require treatment about a month earlier. What condition are you looking at here?

A. Contact dermatitis.
B. Candidiasis.
C. Seborrheic dermatitis.
D. Inverse pityriasis rosea.
E. Psoriasis. 

Case 4: Inverse pityriasis rosea

The development of oval-shaped lesions following an upper respiratory tract infection points to the diagnosis of inverse pityriasis rosea, D—a condition in which pityriasis rosea is confined primarily to the axillary vaults, sometimes including the groin area and generally sparing the trunk. The other conditions in the differential—contact dermatitis, candidiasis, seborrheic dermatitis, and psoriasis—are characterized by confluent rather than multiple discrete lesions.