Unilateral Axillary Pseudochromhidrosis-like Lesion Caused by Pediculosis Pubis.

To the Editor: A 55-year-old homosexual man presented with complaints of right axillary redness for one week. He has been sexually active with a male partner during his travel to South China in hot weather about a month ago. Physical examination revealed redness in his right axillary area, which stained his white clothing [Figure 1a]. A lot of mobile Pthirus pubis insects were visible on his axillary hair in the affected area [Figure 1b and 1c]. Dermatoscopy confirmed the presence of P. pubis on his right axillary hair [Figure 1d]. The patient was found with no other sexually transmitted diseases except P. pubis with a detailed laboratory test and physical examination. Microbiological studies revealed no bacterial or fungal etiology. Cotton stained with axillary sweat was seen. No systemic illnesses, genital lesions, or pruritus outside the axilla area were observed. A diagnosis of P. pubis-related pseudochromhidrosis of the axillary hairs was made. No lice or nits were detected in the beard, armpits, mustache, or eyelashes. No other sexually transmitted diseases were identified. The right axillary area was shaved and treated with 10% sulfur ointment once daily for 3 days. The patient was advised to wash all clothing and fomites with insecticide. The color vanished quickly. Two weeks later, the itching was resolved and the nits disappeared. No relapse or recurrence was observed over a 12-month follow-up.

Figure 1

(a) Red color on the white underwear. (b) Red color and moving pediculosis pubis over the axillary. (c) A lot of moving pediculosis pubis and lice eggs on the axillary hairs in the red area. (d) Pediculosis pubis (with parasitic ovum) under the camera and dermatoscope (Hamamatsu, Japan, original magnification, ×10).

P. pubis, also known as crab louse or pubic louse, is commonly transmitted sexually [1] and may infest pubic hair and perianal areas, legs, forearms, chest, eyebrows, axillary hair and beard, and rarely involves the eyelashes (phthiriasis palpebrarum). Interestingly, the patient showed only unilateral axillary disease. It may be related to the side-sleeping posture or specific sex position. Dermatoscopy enabled identification of the louse.[2] However, a detailed sexual history and lifestyle evaluation are critical. For the management of P. pubis, 0.5% malathion lotion and 5% permethrin cream were recommended based on the new European guidelines.[3] Such patients often have concomitant sexually transmitted disease, warranting screening for HIV, syphilis, gonorrhea, chlamydial infection, herpes, warts, and trichomoniasis.[1] Pseudochromhidrosis is characterized by altered skin pigmentation due to the presence of surface compounds, molecules, or chromogenic bacteria in the sweat.[4] Pseudochromhidrosis occurs when eccrine sweat reacts with dyed clothing, paints, or chromogenic bacteria.[5] P. pubis infections alter the skin color by deep dermal hemosiderin deposition from the bites and may stain the clothes with minute droplets of blood and crusts, prompting medical attention.

In conclusion, we report a case of P. pubis-induced unilateral axillary pseudochromhidrosis-like lesion. P. pubis is a rare clinical disease, usually infected through sexual intercourse. In the differential diagnosis, clinicians should be alert to the possibility of other sexually transmitted diseases.

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