An 84-year-old man presents with pruritic, generalized, erythematous and crusted hyperkeratotic dermatitis. The patient's history is remarkable for laryngeal cancer, chronic obstructive lung disease, chronic renal insufficiency, and long-term prednisone therapy for possible bullous pemphigoid. The photograph demonstrates an erythematous, tense skin surface with severe crusted hyperkeratosis on the patient's hand.

What is the cause of this dermatitis?Norwegian scabies Scrape cytology and subsequent skin biopsy revealed mites, ova, eggshells, fecal pellets, and larvae in the keratin burrow consistent with Sarcoptes scabiei. Norwegian scabies—also known as the 7-year itch, camp itch, gale, Norwegian itch, scabies norvegica, scabies crustosa, and keratotic scabies—is a rare clinical manifestation with S scabiei, typically affecting elderly patients who are immunosuppressed, diabetic, or malnourished. Norwegian scabies is characterized by erythematous, squamous, papular or macular, psoriasislike crusted hyperkeratosis that is not limited to a specific area.

Scrape cytology demonstrates an adult mite (left, Diff-Quik stain, original magnification 31000), and a skin biopsy specimen reveals mites with ova in the keratin burrows (right, hematoxylin-eosin stain, original magnification 3200).(IMAGES: CESAR V. REYES, MD)

This manifestation can be confused with severe eczema, psoriasis, or Darier's disease, and a delayed diagnosis may have serious consequences, including colonization with Staphylococcus aureus, pyoderma, septicemia, and death. Therapeutic trials with scabicides have been used for presumptive clinical diagnosis. Direct examination of the potassium hydroxide preparation or stained-scrape cytology demonstrates embryonated sarcoptic eggs, eggshells, fecal pellets, larvae, and male and female adult mites. A skin biopsy typically reveals numerous organisms in the burrows of the corneal layer. An underlying perivasculitis with a collar of lymphocytes, histiocytes, and numerous eosinophils may also be present. Other histologic findings are spongiotic vesicles, densely cellular nodules, and hyperkeratotic psoriasiform dermatitis.

Treatment Treatment consists of removing all crusted keratin by soaking in warm water and scrubbing with soap. Permethrin 5% cream has been used with success, but more recently ivermectin (Stromectol),* 2 doses of 200 mcg/kg, has been reported to effectively eradicate the organisms.

Preventing contagion Norwegian scabies is highly contagious; estimates are that several thousand mites and ova can be shed from a single patient over 2 days. The adult mites can survive for 3 days and the eggs for up to 10 days without a host, and a single case could cause a large outbreak in a hospital or other institution. Swift diagnosis, appropriate treatment, barrier nursing, and decontamination of the environment are essential to managing an infestation. Thorough hand washing after patient contact, use of gowns and gloves for contact with the lesions, and appropriate treatment, along with vigilance and a high degree of suspicion, are keys to preventing the spread of the organism.

*Unlabeled use.

CESAR V. REYES, MD, Pathologist, Morris Hospital, Morris, Ill.

Ronald G. Wheeland, MD, Department editor Professor and Chief, Section of Dermatology, Department of Medicine, University of Arizona Health Sciences Center, Tucson; and member, Patient Care Subspecialist Advisory Board.