Understanding Scabies and Lice
The Diagnosis — Scabies, Head Lice and Pubic Lice
Accurate diagnosis of scabies and lice infestations is essential for successful treatment of individuals and containment of outbreaks or epidemics in large population groups. While some patients suffering from these highly-contagious health conditions are easily diagnosed, a considerable number of cases are misdiagnosed. This can lead to mismanagement and also contributes to the development of treatment-resistant forms of scabies and lice, which further compromises effective disease control. Click here to learn why second-line treatments are medically necessary for some patients.
An accurate diagnosis of scabies is not always simple
Sometimes, the telltale signs of scabies are readily apparent.1 In other instances, scabies can mimic other skin conditions with similar clinical characteristics.2 A high degree of suspicion of scabies, based on a patient’s history and lifestyle, is necessary for an accurate diagnosis of scabies infestation because of the variety of signs and symptoms that may or may not be present.3
Telltale signs of scabies include:
- Intense itching that worsens at night3
- The appearance of short, wavy, scaly grey lines on the skin due to burrowed scabies mites3
- Symmetrical distribution of scabies rash noted in the web spaces between the fingers, and on the wrists, sides of the hands and feet, elbows, armpits, waist, buttocks, genitals, and breasts/nipples in women3,4
- Secondary infection and eczema from scratching can mask the signs of scabies and complicate diagnosis4
- Papules or nodules (small, solid bumps on the skin), vesicles (small, fluid-filled blisters), and pustules (small, pus-filled blisters) on the skin
- Eczema (itching, scaling and thickening of the skin) resulting from the body’s immune reaction to scabies mites and their fecal matter
Microscopic identification of scabies infestation can pose a challenge—even for highly-trained healthcare professionals—but is the only way to make a definitive diagnosis1
Making a definitive diagnosis of scabies:
- Requires positive identification of scabies mites, their eggs, or fecal matter1
- Scrapings are taken from burrows using a sterile scalpel blade and a drop of mineral oil and then viewed under a microscope1
- Successful sampling and microscopic identification requires considerable skill and practice1
Diagnosing lice infestation can also be challenging
Lice infestations are associated with a range of symptoms or none at all.7 Head lice in particular are often managed in school settings where misdiagnosis is a common problem.8 Moreover, patients may self-medicate with over-the-counter remedies prior to seeing a healthcare provider, which can further obscure diagnosis and proper management.7
Common signs and symptoms of lice infestation:
- Head lice are most easily found on the nape of the neck and on the scalp behind the ears9
- Pubic (crab) lice most often attach to pubic hairs and adjacent hairs of the chest, stomach, legs, and buttocks9
- Symptoms are common and include: itching, inflammation, swollen lymph nodes, bite reactions and rash4,7
Head lice infestation is often misdiagnosed:8
- Research on school “no nit” policies found that non-infested children were actually sent home more frequently than those with active lice infestations because of misdiagnosis8
- The presence of nits on the scalp does not, by itself, indicate the presence of an active head lice infestation7
- Small dried flakes in the hair, such as from hairspray or dandruff, can sometimes be mistaken for louse nits7
Misdiagnosis of lice infestation leads to improper treatment and may also contribute to increased drug resistance8
Definitive diagnosis requires visualization of crawling lice:
- Head lice can be seen with the naked eye crawling on or near the scalp; the use of a comb enhances the ability to identify them7,9
- Pubic (crab) lice and their nits can also be seen with the naked eye; the presence of small grey-blue bite marks is another characteristic sign7,9
- Microscopic examination of hair can also help to confirm a diagnosis of lice7
- Karthikeyan K. Treatment of scabies: newer perspectives. Postgrad Med J. 2005;81:7–11.
- Orion E, Matz H, Wolf R. Ectoparasitic sexually transmitted diseases: scabies and pediculosis. Clin Dermatol. 2004;22(6):513–519.
- Johnston G, Sladden M. Scabies: diagnosis and treatment. British Med J. 2005;331:619–622.
- Habif TP. Scabies. In: Clinical Dermatology, 4th edition. New York: Mosby; 2004:497–505.
- Walton SF, Holt DC, Currie BJ, et al. Scabies: new future for a neglected disease. Adv Parasitol. 2004;57:309–376.
- U.S. Centers for Disease Control and Prevention (CDC). Parasitic Disease Information: Scabies Fact Sheet. 2005. Available at: http://www.cdc.gov/parasites/scabies/epi.html.
- Ko CJ, Elston DM. Pediculosis. J Am Acad Dermatol. 2004;50(1):1–12; quiz 13–4.
- Hansen RC. Overview: the state of head lice management and control. Am J Manag Care. 2004;10(9 Suppl):S260–S263.
- Habif TP. Pediculosis. In: Clinical Dermatology, 4th edition. New York: Mosby; 2004:506–510.