Truncal Demodex Folliculitis

A 42-year-old man with skin-type II was referred to our dermatology outpatient clinic for a 10-year history of a rash on his face, upper chest and upper back. The rash was constantly present and would acutely flare once to twice monthly. These flares would last for several days and would resolve regardless of attempted treatments. During each flare, the rash would become more painful than baseline, with accompanying serous exudate. The patient was unable to identify any triggers for his flares and denied any exacerbation of symptoms by sunlight. He had previously been treated for seborrheic dermatitis and tinea corporis with topical antifungals and eventually oral terbinafine and oral antibiotics without improvement. Various topical steroids provided little improvement and he denied use of topical medications for acne. The patient’s other medications at the time of evaluation were trazodone, quetiapine, sertraline and lisinopril. Exam was remarkable for erythematous plaques with collarettes of scale on the upper chest and upper back, as well as generalized facial erythema without telangiectasias, pustules, or papules (Figure 1). A potassium hydroxide (KOH) stain was negative. A punch biopsy of the mid chest was performed and histopathology revealed a slight spongiotic dermatitis with a sparse superficial perivascular infiltrate and the presence of Demodex mites within the hair follicles (Figure 2). Periodic acidSchiff (PAS) stain was negative for fungus. The patient was given two doses of ivermectin 200 μg/kg one week apart. The patient’s rash resolved completely. At his four-month followup visit, he had no visible rash and no pruritus. Topical sulfur was recommended for treatment should his symptoms return.

A 42-year-old man with skin-type II was referred to our dermatology outpatient clinic for a 10-year history of a rash on his face, upper chest and upper back. The rash was constantly present and would acutely flare once to twice monthly. These flares would last for several days and would resolve regardless of attempted treatments. During each flare, the rash would become more painful than baseline, with accompanying serous exudate. The patient was unable to identify any triggers for his flares and denied any exacerbation of symptoms by sunlight. He had previously been treated for seborrheic dermatitis and tinea corporis with topical antifungals and eventually oral terbinafine and oral antibiotics without improvement. Various topical steroids provided little improvement and he denied use of topical medications for acne. The patient's other medications at the time of evaluation were trazodone, quetiapine, sertraline and lisinopril. Exam was remarkable for erythematous plaques with collarettes of scale on the upper chest and upper back, as well as generalized facial erythema without telangiectasias, pustules, or papules ( Figure 1). A potassium hydroxide (KOH) stain was negative. A punch biopsy of the mid chest was performed and histopathology revealed a slight spongiotic dermatitis with a sparse superficial perivascular infiltrate and the presence of Demodex mites within the hair follicles ( Figure 2). Periodic acid-Schiff (PAS) stain was negative for fungus. The patient was given two doses of ivermectin 200 µg/kg one week apart. The patient's rash resolved completely. At his four-month followup visit, he had no visible rash and no pruritus. Topical sulfur was recommended for treatment should his symptoms return.
Eight months following his initial treatment, the patient experienced a mild recurrence of his symptoms. He was again prescribed a course of oral ivermectin and his rash resolved within a week.

INTRODUCTION
Demodex brevis and Demodex folliculorum are two species of ubiquitous parasites whose role in human disease continues to be fully elucidated. 1,2 Demodex most commonly causes symptomatic infestations confined to the head and neck. 3 Clinically, symptoms may mimic acne vulgaris, papulopustular rosacea, perioral dermatitis, and seborrheic dermatitis, among others. 1-3 Practitioners must maintain a high level of suspicion to avoid misdiagnosis. It has been proposed that up to 80-90% of humans harbor the Demodex mite, which is usually found in the pilosebaceous unit of normal skin and can be found in all ages 1, 4 . Roughly 10% of biopsies from normal skin will contain the Demodex mite 1 . Adults are most commonly diagnosed with Demodex folliculitis and immunosuppression may contribute to cutaneous manifestations of the disease 5 .
Clinically, patients most commonly present with erythematous papules and pustules on hair bearing skin, usually on the face. 1, 2 A KOH stain of affected skin will be positive for Demodex mites, but clinical correlation is necessary because of the high prevalence of Demodex mites in normal skin. Patients can be treated with topical medications such as permethrin or sulfur-containing preparations. Oral ivermectin as two 200 µg/kg doses one week apart can also be effective. 6, 7 Other treatments such as topical lindane & oral metronidazole have also been described. 1,2 This case describes a symptomatic infestation with the Demodex mite below the head and neck. Interestingly, most evidence of follicular involvement on physical examination was confined to the trunk, with only erythema and telangiectasia present on exam of the head and neck. The patient's longstanding symptoms despite numerous treatment attempts with antifungals and antiinflammatories, combined with the complete response to treatment with ivermectin, suggest that the finding of Demodex mites on biopsy was pathologic. This is further supported by our patient's mild recurrence that was easily treated with a second course of ivermectin.
Truncal Demodex has been reported in a small number of cases in the past. 1,2,5,8,9 Increasing awareness of the possibility of symptomatic Demodex infestation below the head and neck can lead to more efficient diagnosis and treatment. The possibility of Demodex folliculitis should be considered in patients with a recalcitrant dermatitis without a clear etiology.