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Traditional acne therapies fail to improve rash on 14-year-old female's nose
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An otherwise healthy 14-year-old female presents to your office for a rash on her nose that has not improved with traditional acne therapies. The patient reports having had acne on her face for about 2 years now. She had initially been treated with a topical retinoid. This helped with the comedones on her forehead, cheeks and chin, but the inflammatory papules and pustules on her nose have continued to slowly progress. After completing a 2-month oral course of doxycycline with no improvement, she was referred for definitive management.
The patient seems sociable and at ease. She reports good adherence to her past acne treatment plans and denies any unusual picking or manipulation behaviors. She has no known allergies and takes no other medications. She has never been sexually active, and she denies a history of recurrent illnesses. She has never traveled outside of the United States, and she lives in an apartment building with the rest of her unaffected family members. Her only known exposure to animals is through her aunt, who works at a plant that specializes in the smoking and salting of fish.
Physical exam shows a healthy-appearing female with a follicular-based, inflammatory popular and pustular eruption concentrated at the middle of her face, localizing mainly to her nose. No comedones — open or closed — are present on her skin. There is no evidence of blepharitis or alopecia. The remainder of her skin exam is remarkable only for how unremarkable it is. She has no lymphadenopathy. Her physical exam is otherwise completely normal.
Figure 1. Figure 1 is a patient with atypical pustuler eruption of the nose.
You decide to perform bacterial, fungal and atypical mycobacterial cultures of the pustules and treat her empirically with a 2-month oral course of trimethoprim-sulfamethoxazole. When she returns to your office for follow-up, her cultures are all negative, and the pustules have not diminished. In fact, both she and you feel her condition may have worsened slightly.
Based on these findings, you begin to widen your differential diagnosis. Which of the following management options would most likely help you to elucidate the true pathogenesis of this patient’s atypical pustular eruption of the nose?
A.Try an empirical 2-month course of oral cephalexin.
B.Perform a skin scraping and plate the contents on a glass slide for microscopic exam.
C.Carefully un-roof a pustule and send the contents for direct fluorescent antibody (DFA) and viral culture.
D.Pay a visit to the aunt’s factory and find out what is so fishy about this story.
Case Discussion
The patient presents with an atypical pustular eruption of the nose and central face that is culture negative and unresponsive to oral antibiotics. An empirical course of cephalexin, as suggested by answer A, would not be expected to improve the patient’s condition any more so than the already attempted doxycycline and TMP-SMX; likewise, empirical treatment gets you no closer to the true pathogenesis of her condition. Answer C offers two methods commonly employed for diagnosing herpes virus infection. Nothing about this patient suggests a herpetic etiology, but it would probably not hurt to send a viral culture as part of her larger workup. Alas, those specific tests would have been negative, as well. Visiting the aunt’s fish factory, as recommended by answer D, would only yield an abundance of red (ie, smoked and salted) Atlantic herrings.
That leaves answer B. You carefully un-roof several of the patient’s pustules with a 15-blade and scrape the skin, plating the contents on a standard glass slide. Microscopy reveals an organism with a flattened head, elongated abdomen and four pairs of short, peg-like legs. You immediately recognize the distinctive features of Demodex folliculorum, a vermiform mite that inhabits the lumen of sebaceous follicles, with a predilection for the larger pilosebaceous units of the nose, forehead, chin and scalp. The mites are commonly seen as “incidental findings” in biopsies of older patients. They have also been implicated as a potential cause (or consequence) of rosacea, although evidence remains controversial. A different species of Demodex mite (D. canis) causes demodectic mange in dogs but does not affect humans.
Figures 2 and 3. Figures 2 and 3 are images of Demodex mites, a vermiform mite that inhabits the lumen of sebaceous follicles. The mites are commonly seen as “incidental findings” in biopsies of older patients.
Source: CDC
Folliculitis caused by the Demodex mite occurs most commonly in the setting of immunosuppression (eg, HIV infection, chemotherapy, leukemia, etc). True infection is extremely uncommon in prepubertal patients with competent immune systems. The finding of extensive Demodex mites in this teenage female prompts you to complete a thorough clinical workup and lab investigation, which thankfully reveals no underlying immunodeficiency.
With the diagnosis made, you initiate targeted therapy. You start with topical metronidazole, which is well tolerated by most people, and the patient begins to respond rapidly. Two weeks later, she has some persistent erythema and several residual pustules, so you change to topical permethrin, applied once weekly for an additional 2 weeks straight. At her most recent follow-up appointment, her lesions have completely cleared with only some residual post-inflammatory hyperpigmentation.