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Pediculosis and Pthiriasis (Lice Infestation) Differential Diagnoses

  • Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD  more...
 
Updated: Feb 05, 2016
 
 

Diagnostic Considerations

True nit infestation must be distinguished from hair casts (pseudonits). Hair casts are ringlike remnants of the inner root sheath of the hair follicle. They are amorphous and freely moveable along the hair fiber.

Many scalp conditions can cause pruritus. Seborrheic dermatitis presents with erythema and scaling. It affects the scalp, eyebrows, nasolabial folds, and central chest. Acne necrotica presents with inflamed follicular papules and pustules, black crusts, and scarring. It is extremely pruritic, and patients usually pick at the lesions.

Free-living primitive psocid lice feed on decaying matter in leaves, old books, and animal habitats. They may cause human scalp infestation in children when they visit a library or doghouse that is infested. Psocids have large heads with massive jaws, large hind legs, and long antennae and are distinguished easily from Anoplura lice.[6]

Other problems to be considered in the differential diagnoses of head louse infestation include the following:

  • Dandruff
  • Dried hairspray/gel
  • Dermatophyte infection
  • Piedra (black piedra from Piedraia hortae, white piedra from Trichosporon asahii and other species of Trichosporon)
  • Hair shaft abnormalities (ie, monilethrix, trichorrhexis nodosa)
  • Delusions

Other problems to be considered in the differential diagnoses of body louse infestation include the following:

Other problems to be considered in the differential diagnoses of pubic louse infestation include the following:

 
 
Contributor Information and Disclosures
Author

Lyn C C Guenther, MD, FRCPC, FAAD Medical Director, The Guenther Dermatology Research Centre; President, Guenther Research, Inc; Professor, Department of Medicine, Division of Dermatology, Western University of Health Sciences, Canada

Lyn C C Guenther, MD, FRCPC, FAAD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Society for Dermatologic Surgery, Association of Professors of Dermatology, Canadian Dermatology Association, Canadian Dermatology Foundation, Canadian Medical Association, Canadian Society for Dermatologic Surgery, College of Physicians and Surgeons of Ontario, Drug Industry Association, European Academy of Dermatology and Venereology, International Hyperhidrosis Society, International League of Dermatological Societies, International Society for Dermatologic Surgery, London and District Academy of Medicine, Ontario Medical Association, Royal College of Physicians and Surgeons of Canada, Society for Investigative Dermatology, Society for Pediatric Dermatology

Disclosure: Received consulting fee for consulting for: Johnson & Johnson; L'Oreal.

Coauthor(s)

Sheilagh Maguiness, MD FRCPC, FAAD, Pediatric Dermatologist, Boston Children's Hospital

Sheilagh Maguiness, MD is a member of the following medical societies: American Academy of Dermatology, Canadian Medical Association, Society for Pediatric Dermatology, Women's Dermatologic Society, Canadian Dermatology Association

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Chief Editor

Michael Stuart Bronze, MD David Ross Boyd Professor and Chairman, Department of Medicine, Stewart G Wolf Endowed Chair in Internal Medicine, Department of Medicine, University of Oklahoma Health Science Center; Master of the American College of Physicians; Fellow, Infectious Diseases Society of America

Michael Stuart Bronze, MD is a member of the following medical societies: Alpha Omega Alpha, American Medical Association, Oklahoma State Medical Association, Southern Society for Clinical Investigation, Association of Professors of Medicine, American College of Physicians, Infectious Diseases Society of America

Disclosure: Nothing to disclose.

Acknowledgements

Thomas W Austin, MD Professor Emeritus, Department of Medicine, Division of Infectious and Sexually Transmitted Diseases, University of Western Ontario, Canada

Thomas W Austin, MD is a member of the following medical societies: Canadian Infectious Disease Society, College of Physicians and Surgeons of Ontario, Ontario Medical Association, and Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

David F Butler, MD Professor of Dermatology, Texas A&M University College of Medicine; Chair, Department of Dermatology, Director, Dermatology Residency Training Program, Scott and White Clinic, Northside Clinic

David F Butler, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, American Society for Dermatologic Surgery, American Society for MOHS Surgery, Association of Military Dermatologists, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Edward F Chan, MD Clinical Assistant Professor, Department of Dermatology, University of Pennsylvania School of Medicine

Edward F Chan, MD is a member of the following medical societies: American Academy of Dermatology, American Society of Dermatopathology, and Society for Investigative Dermatology

Disclosure: Nothing to disclose.

Pamela L Dyne, MD Professor of Clinical Medicine/Emergency Medicine, David Geffen School of Medicine at UCLA; Attending Physician, Department of Emergency Medicine, Olive View-UCLA Medical Center

Pamela L Dyne, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Dirk M Elston, MD, Director, Ackerman Academy of Dermatopathology, New York

Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

Joseph F John Jr, MD, FACP, FIDSA, FSHEA Clinical Professor of Medicine, Molecular Genetics and Microbiology, Medical University of South Carolina; Associate Chief of Staff for Education, Ralph H Johnson Veterans Affairs Medical Center

Disclosure: Nothing to disclose.

Daniel J Hogan, MD Clinical Professor of Internal Medicine (Dermatology), Nova Southeastern University College of Osteopathic Medicine; Investigator, Hill Top Research, Florida Research Center

Daniel J Hogan, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Contact Dermatitis Society, and Canadian Dermatology Association

Disclosure: Nothing to disclose.

Edmond A Hooker II, MD, DrPH, FAAEM Assistant Professor, Department of Emergency Medicine, University of Cincinnati College of Medicine

Edmond A Hooker II, MD, DrPH, FAAEM is a member of the following medical societies: American Academy of Emergency Medicine, American Public Health Association, Society for Academic Emergency Medicine, and Southern Medical Association

Disclosure: Nothing to disclose.

Abdul-Ghani Kibbi, MD Professor and Chair, Department of Dermatology, American University of Beirut Medical Center, Lebanon

Disclosure: Nothing to disclose.

Rick Kulkarni, MD

Rick Kulkarni, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, American Medical Informatics Association, Phi Beta Kappa, and Society for Academic Emergency Medicine

Disclosure: WebMD Salary Employment

David A Peak, MD Assistant Residency Director of Harvard Affiliated Emergency Medicine Residency, Attending Physician, Massachusetts General Hospital; Consulting Staff, Department of Hyperbaric Medicine, Massachusetts Eye and Ear Infirmary

David A Peak, MD is a member of the following medical societies: American College of Emergency Physicians, American Medical Association, Society for Academic Emergency Medicine, and Undersea and Hyperbaric Medical Society

Disclosure: Nothing to disclose.

Nelly Rubeiz, MD Consulting Staff, Department of Dermatology, American University of Beirut Medical Center; Associate Professor, Department of Dermatology, American University of Beirut, Lebanon

Nelly Rubeiz, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology

Disclosure: Nothing to disclose.

Robert A Schwartz, MD, MPH Professor and Head, Dermatology, Professor of Pathology, Pediatrics, Medicine, and Preventive Medicine and Community Health, UMDNJ-New Jersey Medical School

Robert A Schwartz, MD, MPH is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Physicians, and Sigma Xi

Disclosure: Nothing to disclose.

Russell W Steele, MD Head, Division of Pediatric Infectious Diseases, Ochsner Children's Health Center; Clinical Professor, Department of Pediatrics, Tulane University School of Medicine

Russell W Steele, MD is a member of the following medical societies: American Academy of Pediatrics, American Association of Immunologists, American Pediatric Society, American Society for Microbiology, Infectious Diseases Society of America, Louisiana State Medical Society, Pediatric Infectious Diseases Society, Society for Pediatric Research, and Southern Medical Association

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Jeter (Jay) Pritchard Taylor III, MD Compliance Officer, Attending Physician, Emergency Medicine Residency, Department of Emergency Medicine, Palmetto Health Richland, University of South Carolina School of Medicine; Medical Director, Department of Emergency Medicine, Palmetto Health Baptist

Jeter (Jay) Pritchard Taylor III, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American Medical Association, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Mary L Windle, PharmD Adjunct Associate Professor, University of Nebraska Medical Center College of Pharmacy; Pharmacy Editor, Medscape

Disclosure: Nothing to disclose.

Wayne Wolfram, MD, MPH Associate Professor, Department of Emergency Medicine, Mercy St Vincent Medical Center

Wayne Wolfram, MD, MPH is a member of the following medical societies: American Academy of Emergency Medicine, American Academy of Pediatrics, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Neil W Yoder, DO Staff Physician, Department of Emergency Medicine, St Vincent Mercy Medical Center

Neil W Yoder, DO is a member of the following medical societies: American College of Emergency Physicians and Emergency Medicine Residents Association

Disclosure: Nothing to disclose.

Jeffrey M Zaks, MD Clinical Associate Professor of Medicine, Wayne State University School of Medicine; Vice President, Medical Affairs, Chief Medical Officer, Department of Internal Medicine, Providence Hospital

Jeffrey M Zaks, MD is a member of the following medical societies: American College of Cardiology, American College of Healthcare Executives, American College of Physician Executives, and American Medical Association

Disclosure: Nothing to disclose.

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Nit on a hair. Note the thin, translucent cement surrounding the hair shaft. Photo courtesy of David Shum, MDWestern University, London Ontario.
Two empty nits from Pediculus humanus capitis. Note the open shells still attached to the hairs and the porous operculi through which the lice have hatched. Photo courtesy of David G. Schaus.
Three specimens of Pediculus humanus capitis.
Pediculus humanus corporis.
Phthirus pubis. Note the crab-like appearance.
The head louse, Pediculus humanus capitis, has an elongated body and narrow anterior mouthparts. Body lice look similar but lay their eggs (nits) on clothing fibers instead of hair fibers.
The pubic louse, Pthirus pubis, is identified by its wide crablike body.
 
 
 
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