Demodicosis Imitating Acne Vulgaris: A Case Report

Introduction

Demodex is a genus of mites that live in the pilosebaceous unit of mammals as a normal flora. In special circumstances, Demodex mite can cause multiple skin disorders grouped under the term demodicosis or demodicidosis, which has various clinical features based on the literature. For example, pityriasis folliculorum type manifests as erythematous patch with dry, sandpaper-like rough skin due to the increased scale within hair follicles.^1,2 Rosacea-like type consists of itchy, burning, erythematous skin with papulopustular lesions involving the face of patients, with or without pre-existing rosacea.^3,4 Folliculitis-like type is described as localized follicular pustules that mimic acne vulgaris or folliculitis.^2,5 Perioral dermatitis-like type has the appearance of papulopustular lesions involving the perioral area like perioral dermatitis.⁶ This report describes a young woman who initially developed clinical symptoms of pityriasis folliculorum type demodicosis which turned into folliculitis-like type demodicosis, imitating acne vulgaris.

Case Report

A healthy 19-year-old woman presented with dry, itchy rash with multiple small edematous papules and pustules on both cheeks for four weeks. One year ago, this patient had a history of recurrent unexplained eczematous rash on her face that had a good response to topical 0.1% triamcinolone cream and relapsed immediately after treatment. Skin examination revealed dry erythematous patch, rough skin with “sandpaper-like” texture on her face. An abnormally high density of Demodex mites was detected with more than 5 Demodex mites/cm² from rash on her cheeks by standardized skin surface biopsy. Based on clinical symptoms and laboratory test, the patient was diagnosed with pityriasis folliculorum type demodicosis and treated with two doses of oral ivermectin (200 μg/kg per dose, 1 week apart) and topical 0.75% metronidazole gel for 4 weeks. After the treatment, all clinical symptoms disappeared without using any other topical medications. Six weeks ago, the patient began to develop dry itchy rash on her face (Figure 1), and two weeks later multiple small erythematous papules and pustules gradually appeared on both cheeks. The patient did not have a history of using new cosmetic products or any other topical treatment before the symptoms manifested. Physical examination revealed dry, patchy erythematous patch on face and upper part of the neck combined with multiple small edematous erythematous papules and minute whitish papules, size 3–5 mm, discrete on both cheeks (Figure 2). The patient was first diagnosed as acne vulgaris and treated with doxycycline 100 mg twice a day for 2 weeks, but the clinical symptoms did not show any signs of improvement. Laboratory investigations were performed to determine the cause of rash and pustules on the face. Standardized skin surface biopsy from the rash with microscopic examination found 8 Demodex mites/cm² of sampling area (Figure 3). Superficial needle-scraping with methylene blue staining was used to determine the cause of pustules. Five Demodex mites were detected from five pustular lesions on both cheeks (Figure 4A–C). Based on clinical symptoms and laboratory findings, the patient was diagnosed with folliculitis-like type demodicosis and was treated with 2 doses of oral ivermectin (200 μg/kg, 1 week apart) in combination with moisturizer and topical 0.75% metronidazole gel. Most of the erythematous papules, pustules and dry erythematous patch gradually resolved in 2 weeks after treatment had started. All clinical symptoms disappeared in an additional two weeks with topical 0.75% metronidazole gel treatment.

Figure 1 Dry erythematous patch, follicular scales and rough skin with “sandpaper-like” texture on the right cheek.

Figure 2 Dry, patchy erythema on face and upper part of the neck combined with multiple small edematous erythematous papules and minute whitish papules, size 3–5 mm, discrete on the right cheek.

Figure 3 Multiple Demodex mites are detected by standardized skin surface biopsy from the rash on the right cheek.

Figure 4 (A–C) Demodex mites are detected by superficial needle-scraping with methylene blue staining from pustular lesions on both cheeks.

Discussion

Demodex mites are common ectoparasites in human skin. Studies have shown that the number of mites increases with age and is found to be significantly higher in people with obesity, high blood sugar levels, end-stage chronic renal failure and immunodeficiency.^7–9 In addition, an abnormal increase in the number of Demodex mites has been reported following repeated facial application of topical steroids and other immunomodulators.¹⁰ Changing in facial skin microenvironment, moisture, pH levels, types and quantities of skin surface lipids and epidermal barrier function may facilitate Demodex mite proliferation.¹¹ The Demodex mite can cause multiple skin disorders, which are grouped under the term demodicosis or demodicidosis. Some studies have shown an association between acne vulgaris and Demodex mite infestation, suggesting that when conventional treatments for acne vulgaris are ineffective, examination of Demodex mites and acaricidal therapies should be considered.^2,12 This report demonstrates a case of demodicosis presenting with clinical symptoms that looked like acne vulgaris, including erythematous edematous papules and pustules on both cheeks, leading to the difficulty in differential diagnosis. Therefore, the method used to determine the mite density per square centimeter is important for diagnosing demodicosis. Standardized skin surface biopsy (SSSB) is commonly used to determine Demodex mite density from skin of the patients. Demodicosis is diagnosed when there is a high density of Demodex mites (>5 Demodex mites/cm²).¹³ A method for assessing Demodex mite density in papulopustular lesions, called “superficial needle-scraping” (SNS), is performed by scraping off 5 small pustules with the tip of a needle for microscopic examination. Demodex mite density was reported as “mites per 5 pustules” for SNS. Demodicosis is diagnosed when there is a high density of Demodex mites, at ≥3 Demodex mites per 5 pustules.¹⁴ In this patient, the results of microscopic examination revealed an abnormal increase in the number of Demodex mites from both SSSB and SNS methods and, combined with the relevant clinical presentations, led to the diagnosis of folliculitis-like demodicosis. Treatment with acaricides for demodicosis is expected to reduce the excessive number of Demodex mites and recover the patients from clinical symptoms. The following topical medications have been reported to be effective for demodicosis: metronidazole, permethrin, benzoyl benzoate, crotamiton, lindane, tea tree oil and ivermectin. All topical treatments should be used with caution, because of the sensitive skin in demodicosis patients, and many topical therapies have also been associated with mild irritation.¹⁵ Oral medication should be considered in patients with severe symptoms or not responding to topical therapy. Oral metronidazole has shown efficacy in reducing Demodex mite density and improving clinical symptoms of demodicosis.¹⁶ Ivermectin and fluralaner can inhibit overlapping molecular pathways regulating neuron activity, causing paralysis, lack of feeding and indirect killing effect on the Demodex mite, so they can be used to treat demodicosis without side effects to the human body.^17,18 Last year, this patient had a history of pityriasis folliculorum type demodicosis and successful treatment with oral ivermectin. This time, the patient still responded well to oral ivermectin and metronidazole gel treatment despite the changes in clinical type of demodicosis from pityriasis folliculorum type to folliculitis-like type, which imitated acne vulgaris.

Conclusion

Demodicosis is not an uncommon skin disease and can show a variety of clinical symptoms that dermatologists are not familiar with, making it often misdiagnosed or underdiagnosed. This is a case report of demodicosis presenting with multiple edematous erythematous papules and pustules on both cheeks, misdiagnosed as acne vulgaris. After reassessment based on clinical presentation and laboratory examination that found multiple Demodex mites from pustules and rash on both cheeks, the patient was diagnosed with folliculitis-like demodicosis imitating acne vulgaris. Demodicosis can occur whenever there is an imbalance between microenvironment, density of Demodex mites and host immunity. Moreover, the clinical presentation of demodicosis can change from one type to another, as in this patient, changing from pityriasis folliculorum type to folliculitis-like type.