Uncommon presentation: Pubic lice infesting beard in a patient with neurodegenerative disorder

An 82-year-old male with a non-specific neurodegenerative disorder presented with mild irritation in his beard. During the clinical examination, blackish, stuck-on lesions were observed in the patient’s beard and chest, which could be easily scraped off [Figure 1a]. Dermoscopic examination revealed live lice clinging to the surrounding body hair confirming the diagnosis of crab lice infestation [Figure 1b]. The patient was treated with topical 1% permethrin lotion, two local applications a week apart.

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Figure 1:

(a) Blackish stuck structures on the skin of the beard and multiple nits clinging to hair. (b) Dermoscopy (DermLite II Hybrid M Dermatoscope at ×10 magnification in polarized mode) shows crab louse clinging on to hair.

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Phthirus pubis or crab louse is a tiny parasite measuring 1.25–2 mm in length. It has an oval body resembling a crab with a smaller head and three pairs of legs. This louse is typically found in apocrine gland-bearing areas such as the genital, perianal, and groin regions but can also infest less common areas such as the chest, axilla, mustache, and beard. Diagnosis is based on the identification of adult lice and nits (lice eggs) on hair. Entomodermoscopy can be used as a rapid diagnostic tool. On dermoscopy, Phthirus pubis appears light colored, has a smaller size (1•2 × 8 mm), and has slow motility as compared to the brown color, larger size, and quick motility of Pediculus humanus (human head and body lice). In addition, P. pubis appears such as pincers of a crab due to the thicker posterior pair of legs than the front pair giving it an appearance similar to the pincers of a crab.^[1]

This case highlights the importance of prompt diagnosis and appropriate treatment for parasitic infestations such as crab lice, especially in individuals with compromised health or in vulnerable populations. It is crucial to follow the recommended treatment protocols and take measures to prevent further transmission.