These nine cases will test your ability to distinguish ringworm from infections that can cause similar eruptions. See how many diagnoses you get right.

Even though tinea infection is a common cause for a patient’s presenting with single or multiple annular lesions, it is just one of several etiologies to consider.

Clinicians need to keep a differential diagnosis in mind, particularly in cases that do not respond to antifungal therapy. A variety of annular lesions have been documented as being linked to drug reactions, infections (mycobacterial, bacterial, fungal), and rheumatologic or inflammatory causes. Using a systematic diagnostic approach, the clinician should be able to determine the exact etiology of an annular lesion. In this article, nine case histories are used to help you distinguish between true tinea and other conditions and to outline the best treatments for each.

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Case 1

An 11-year-old girl visited her grandparents’ farm. About six weeks later, she developed an annular rash that started on her face and began to spread. It was mildly pruritic.

What is the first lab test you should perform?

In most annular lesions for which the diagnosis is uncertain, a skin scraping should be obtained and tested with KOH to determine if the etiology is fungal. The child has been around farm animals that could have exposed her to a fungus. Typical fungal lesions are annular with scale on the leading edge of the lesion, mildly pruritic, and KOH-positive. The KOH in this case was positive.

What is your diagnosis?

The child has tinea corporis or, more specifically, tinea faciale.

What are your treatment options?

One or two localized lesions can be treated with topical imidazole agents or topical terbinafine. If multiple lesions are present or there are lesions at different sites of the body, an oral antifungal may be needed. Griseofulvin, oral terbinafine, or oral triazoles are acceptable agents.

Case 2

A 17-year-old white male presents with a rash on his trunk that has persisted for three weeks. One lesion appeared first, followed by a sudden eruption seven days later of multiple smaller lesions that followed the skin lines. He complains that the rash is mildly pruritic. On questioning, he reports a sore throat about a week before the rash started. The KOH is negative.

What is your diagnosis?

The lesion is ovoid and annular with an inverse collarette of scale. The scale has a trailing edge—i.e., the free edge of the scale points toward the center and is slightly behind the leading edge of the lesion. This appearance is classic for pityriasis rosea. Other clues to the diagnosis is appearance of the herald patch, or first lesion, 7-10 days before the eruption of multiple smaller lesions. A prodrome of a sore throat or upper respiratory infection is also common. Some drugs have been shown to cause a rash similar to pityriasis rosea. Ask the patient about newly started medications.

What lab test should you order?

Since the rash of secondary syphilis can mimic the rash of pityriasis rosea in patients who are sexually active, participate in unprotected intercourse, or have a rash on the palms and soles, a rapid plasma reagin (RPR) or Venereal Disease Research Laboratory test (VDRL) should be obtained.

What are your treatment options?

Pityriasis rosea is self-limiting; the rash should resolve within eight weeks. If the pruritus is bothersome, calamine lotion or another antipruritic topical agent may be used and, if necessary, oral antihistamines. In cases of extensive eruptions, UV therapy has been shown to shorten the duration of the rash. If pityriasis rosea lasts longer than three months, the patient should be counseled to return for a biopsy or be referred to dermatology to rule out other dermatitides.

Case 3

A 28-year-old man presents with a rash that has been present on his palms and soles for three weeks (Figure 3). He recalled myalgias and swollen lymph nodes before the rash developed. The KOH is negative.

What additional information do you need?

The rash looks like that seen in pityriasis rosea but is located on the palms and soles. The patient also had flulike symptoms and adenopathy. Because of these findings, a history of unprotected intercourse and/or a history of a painless penile or mucous membrane ulcer or chancre would assist in making the diagnosis.

What lab test should you order?

An RPR or VDRL. In this case, the VDRL was positive.

What is your diagnosis?

Secondary syphilis.

How is it treated?

The therapy of choice is penicillin, provided as weekly injections for three weeks, or doxycycline for those allergic to penicillin. Patients should be followed with repeat RPRs at three and six months to determine whether additional treatment is needed. The Jarisch-Herxheimer reaction may occur in some patients, usually within several hours of treatment. The patient will develop fever, chills, malaise, myalgias, and arthralgias that generally last 24 hours.

Case 4

A 3-year-old presents with a rash that erupted suddenly. The multiple, small lesions are round with a pink-to-red base and have a silvery-to-white scale on top. They are seen predominantly on the trunk but also involve the arms and legs. The mother states the child has not been eating well for the last couple of days and is febrile. She also notes the child has not been scratching the lesions. KOH is negative.

What is your diagnosis?

A suddenly erupting rash with the appearance of psoriatic plaques is a variant called guttate psoriasis.

What test would you perform?

Guttate psoriasis tends to occur in the presence of an underlying infection, most commonly streptococcal pharyngitis. Therefore, a rapid streptococcal test should be obtained. In this case, it was positive. Once the streptococcal pharyngitis is treated, the psoriatic lesions will recede. An estimated 33%-68% of patients with guttate psoriasis will go on to develop the typical plaques of psoriasis on the extensor surfaces of the elbows and knees, scalp, sacral area, palms, and soles. Importantly, the underlying infection does not cause psoriasis, it merely causes the explosive onset of the guttate variant.

Case 5

A 56-year-old white woman presents with a lesion on her right shin. It has been present for the past year and appears to the patient to be getting larger. It is nonpruritic and causes no pain. When treatment with an OTC antifungal was unsuccessful, she used the triamcinolone 0.1% cream that her primary-care provider gave her. There was no change in the lesion. KOH is negative.

What is your diagnosis?

An asymptomatic lesion on a sun-exposed area of skin that does not respond to topical steroids or antifungal agents is suspicious for skin cancer. The lesion does not have the classic rolled border seen in basal cell carcinoma, raising suspicions of Bowen’s disease or squamous cell carcinoma in situ.

How would the diagnosis be confirmed?

A shave biopsy, which confirmed Bowen’s disease.

Case 6

A 28-year-old woman presents with targetoid lesions on the lower legs (Figure 6). She states the pruritic lesions appear approximately once a month, then resolve only to return again. There are no oral lesions. She takes no medications. KOH is negative.

What is your diagnosis?

The presence of targetoid lesions is most commonly due to erythema multiforme (EM) and, in the absence of mucosal involvement, would be classified as EM minor.

What is the most likely underlying etiology?

EM minor can occur due to underlying infection or medication use. The most common cause for recurrent EM minor is herpes simplex virus (HSV) infection.

What should you do next?

If the recurrent EM is secondary to HSV and the outbreaks are frequent, provide prophylactic treatment to halt recurrent infections. EM secondary to other infections will resolve with adequate treatment of the infection. Suspected medications should be discontinued. The treatment of mild symptoms of EM includes antihistamines, topical steroids, and antipyretics. More severe symptoms may require hospitalization, systemic steroids, and antibiotics.

Case 7

A 26-year-old woman presents with a pruritic annular lesion (Figure 7) that appeared on her hand three weeks ago. There is a prominent indurated border. KOH is negative.

What is your diagnosis?

An annular lesion with an indurated border is rarely fungal in origin. A biopsy is necessary to make the diagnosis, but based on the appearance and presentation, granuloma annulare should be suspected.

What other diagnoses should be considered?

Inflammatory tinea infection, erythema chronicum migrans (Lyme disease), and sarcoidosis should all be included in the differential diagnosis.

For what systemic diseases might a patient with granuloma annulare be at risk?

Patients with granuloma annulare, particularly when they have multiple lesions, are at increased risk of diabetes mellitus or rheumatoid arthritis.

Case 8

A 46-year-old African-American woman presents with indurated, reddish-brown lesions on the central portion of the face (Figure 8). KOH is negative.

What is your diagnosis?

A middle-aged African-American female with indurated, annular skin lesions has sarcoidosis until proven otherwise.

What tests may help you make a diagnosis?

Patients with sarcoidosis may have elevated angiotensin-converting enzyme levels. Pulmonary infiltrates may be visible on chest x-ray. A skin biopsy will confirm the diagnosis of sarcoidosis.

How should the patient be treated?

For patients with cutaneous involvement alone, intralesional or topical steroids are recommended. With ocular or active pulmonary disease, antimalarials, methotrexate, systemic corticosteroids, or other immunosuppressive agents may be considered.

Case 9

A 52-year-old man presents with multiple lesions on the sun-exposed areas of his skin, particularly the lower extremities. The pink-to-red lesions are asymptomatic, but he is unhappy with their appearance, which is slightly atrophic with a threadlike border at the periphery. KOH is negative.

What is your diagnosis?

The key to the diagnosis is the threadlike border and slight atrophy. This is consistent with disseminated superficial actinic porokeratosis (DSAP).

How would you confirm the diagnosis?

A biopsy will confirm the diagnosis, but the clinical findings are usually characteristic.

What are the other diagnostic considerations?

Included in the differential are actinic keratoses, seborrheic keratoses, stucco keratoses, and flat warts.

What are the treatment options?

DSAP can be treated with emollients, keratolytic agents, 5-fluorouracil, or oral retinoids. The patient should be counseled to avoid UV exposure, which will exacerbate the unsightliness of the lesions.

While tinea infection is a common cause of annular skin lesions, consideration of other possible diagnoses is necessary. In a superficial annular lesion with scale, first obtain a KOH. If it is positive, the condition is most likely fungal in origin. There is a possibility that the lesion is superinfected or colonized with fungal elements. Therefore, obtain a culture to confirm your diagnosis.

If the KOH is negative, the history and distribution of the lesions will generally lead the clinician to the correct diagnosis. If the lesions appear inflammatory or indurated, a biopsy will usually be required to determine the etiology. KOH-negative lesions on sun-exposed surfaces that do not respond to topical steroids need to be biopsied to determine if they are neoplastic. However, if multiple, KOH-negative lesions on sun-exposed areas have a threadlike border, DSAP should be considered.

Ms. DiBaise is an adjunct assistant professor at the Arizona School of Health Sciences, A.T. Still University, in Mesa.