Phthiriasis pubis of the eyelashes: Diagnostic clues and management strategies

A 36-year-old male presented with a 2-week history of itching and redness in the right eye. Slit-lamp examination demonstrated multiple crab-like, blackish lice and nits firmly adherent to the roots and shafts of the eyelashes of the right eye. The lice and nits were carefully removed with fine forceps. Light microscopy of the eyelashes confirmed the diagnosis of Phthirus pubis (crab louse) infestation [Figs. 1 and 2]. The patient was subsequently referred to a dermatologist, who initiated systemic ivermectin and permethrin for the genital area involvement along with topical paraffin for eyelash application. Eye quietened and the patient was also counseled regarding maintenance of personal hygiene, disinfection of clothing and bedding, and the importance of screening family members for infestation.Figure 1: Slit-lamp photographs of the right eye showing Phthirus pubis infestation of the eyelashes. (a) Multiple crab lice and nits attached to the roots and shafts of the eyelashes along the lid margin. (b) Magnified view demonstrating adult lice firmly anchored to the hair shafts with adherent ovoid nitsFigure 2: Gross microscopic examination from eyelash of the right eye showing lice with six legs with a thicker posterior pair of legs confirming crab louseDiscussion Among human lice, Pediculus capitis (head louse) and Pediculus corporis (body louse) typically infest the scalp and body hair, respectively, and do not involve the eyelashes.[1] In contrast, Phthirus pubis can infest eyelashes and eyelids (Phthiriasis palpebrarum). The incidence has been reported to range from 0.3% to 4.6%, and the overall prevalence in adults is estimated at around 2%.[1] It is an infrequent cause of eyelid irritation, often overlooked due to its clinical resemblance to more common conditions such as blepharitis and demodicosis. Although this parasite typically inhabits coarse body hair in the pubic region, it may spread to the eyelashes through autoinoculation, intimate contact, or contaminated linens. The management of Phthiriasis palpebrarum requires a meticulous and targeted approach. Mechanical removal of lice and nits with fine forceps remains the mainstay of initial therapy. In this case, adjunctive application of paraffin ointment was prescribed to suffocate any remaining lice and facilitate their removal. Because eyelash involvement often reflects more widespread infestation, dermatological referral is necessary. Systemic ivermectin and topical permethrin for concurrent genital involvement was started by the dermatologist, highlighting the need for comprehensive management beyond the ocular findings. A critical aspect of treating phthiriasis is preventing reinfestation. Patients must be counseled regarding hygiene measures, including thorough washing or heat disinfection of clothing, towels, and bedding. Household contacts and close partners should also be screened and treated, if necessary, as asymptomatic carriers may perpetuate transmission.[2] Important differential diagnosis is demodicosis caused by Demodex mites and Staphylococcal blepharitis. While both can present with itching, redness and lash involvement, subtle differences in the clinical appearance can aid clinical diagnosis. Staphylococcal disease typically presents bilaterally, whereas Phthirus pubis and Demodex infestations may present either unilaterally or bilaterally. In Phthiriasis pubis infestation, the eyelash shafts are covered with blackish-brown nits, giving the lashes a characteristic “powdered” appearance.[3] In contrast, Demodex infestation shows cylindrical collarettes at the lash base, which are waxy and composed of accumulated undigested material, keratinized cells, dead or living mites, and their eggs and egg casings.[2] The chronic form of staphylococcal blepharitis can sometimes mimic these ectoparasites and typically presents with persistent scaling, crusting, and redness of the eyelid margins, often most noticeable upon waking. Accumulated staphylococcal debris mixed with white blood cells forms firm, brittle, fibrinous scales at the lash bases, which may migrate along the lash shaft as it grows. Thickening of the eyelid margin and eyelashes is also commonly observed in Staphylococcal blepharitis.[4] A few rare cases have reported coinfection with Demodex and phthiriasis, where symptoms persisted despite manual nit removal and iodine irrigation and microscopic examination later confirmed coinfestation.[5] Detailed history and careful evaluation of the lid margins and lashes can give clue to the diagnosis.