Pediculosis and Pthiriasis (Lice Infestation) Workup

Updated: Feb 15, 2023
  • Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD  more...
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Approach Considerations

Because the diagnosis of infestation requires identification of a live louse and/or a viable nit, examining suggestive particles under the microscope confirms the diagnosis. Cellulose tape can be applied over an infested area to pick up lice and place them on a microscopic slide to be examined. A Wood lamp examination of the area considered to be infested shows yellow-green fluorescence of lice and nits. Dermoscopy of nymph-containing eggs show ovoid and brown coloration that can be used to reliably differentiate nymph-containing eggs from empty cases or pseudonits. On dermoscopy empty cases are translucent. Pseudo-nits do not have particular dermoscopic findings and are not attached to the hair shaft.  [37]

Infestation with P pubis is an STD, and 30% of these patients have an additional STD. [6]  Thus, it is appropriate to screen these patients for other STDs, including human immunodeficiency virus (HIV), syphilis, gonorrhea, chlamydia, genital herpes, and trichomoniasis.

Scrapings for a fungal culture can be collected if dermatophyte infection is in the differential diagnoses. This is useful when the diagnosis is unclear (ie, no nits or lice have been identified).

Properly evaluating persons who have been raped is essential. Evidence should be collected in such a way as to avoid contamination and to ensure a legal chain of custody. Human DNA can now be identified in the blood present in a pubic louse. Lice recovered after an attack have the potential to provide evidence valuable in securing a conviction.

Histology is rarely required for diagnosis. Examination of a bite shows intradermal hemorrhage and a deep, wedge-shaped infiltrate with many eosinophils and lymphocytes.