Sir,

Human scabies is a widespread parasitic infestation caused by the mite Sarcoptes scabiei, which may vary in impact and presentation depending on the clinical context. Transmission primarily occurs through close contact with an infested individual or by sharing living spaces. Scabies is categorized into two main forms: classic scabies and crusted scabies, or Norwegian scabies [1,2].

Crusted scabies, which is less common, results from a severe infestation where the host’s immune response fails to control the proliferation of mites [3]. This form is marked by the presence of papules, blood crusts, pustules, small vesicles, and burrows. The characteristic grooves of the disease may not always be visible or may become hyperkeratotic, and the skin may appear erythematous with psoriatic plaques, featuring thick, yellowish scales, giving a crusted appearance [4].

While the hands and feet are commonly affected, severe cases may involve almost the entire body surface. If left untreated, secondary bacterial infections may develop, potentially leading to sepsis with a high fatality rate. Severe itching is common, though not always present [5].

Early diagnosis may be challenging due to its rarity and atypical presentation, and it may be mistaken for other skin conditions, such as psoriasis, atopic dermatitis, tinea corporis, or skin malignancies [5]. Diagnosis is confirmed through direct microscopic examination using 10% potassium hydroxide (KOH) to identify mites, eggs, or fecal pellets. A negative KOH preparation does not exclude scabies, yet dermoscopy may serve as an additional diagnostic tool. Often, diagnosis is confirmed by a positive response to treatment [3,4].

In cases where diagnosis is uncertain or treatment response is inadequate, a skin biopsy may prove useful. This is diagnostic if parasites or characteristic epidermal changes, such as acanthosis, hyperkeratosis, thickened stratum corneum, and multiple burrows, are identified [3].

Crusted scabies is particularly common in individuals with compromised cell-mediated immunity, such as those with HIV/AIDS, diabetes mellitus, organ transplant recipients, and those on systemic or topical corticosteroids. Mechanical removal of mites and eggs through scratching is an effective way to limit mite proliferation, so individuals with cognitive impairments, physical disabilities, or neuropathies who cannot feel or interpret itching or scratch effectively are at higher risk for developing crusted scabies [3,6].

Type 2 diabetes mellitus is a significant risk factor for crusted scabies due to chronic hyperglycemia, which adversely affects immune function. Additionally, peripheral neuropathy may impair cutaneous sensation, making it difficult for individuals to remove mites through scratching [5].

Treatment is challenging due to the large number of parasites present in skin scales and crusty lesions. Current guidelines recommend ivermectin at a dose of 200 μg/kg twice a week, with a week between doses. In severe cases, oral ivermectin at 200 μg/kg is recommended on days 1, 2, and 8. If the infestation persists, additional doses on days 9 and 15, or even on days 9, 15, 22, and 29, may be necessary. Up to 92.5% of patients have been cured with two or three doses of this medication [4,7].

A 42-year-old female patient with controlled diabetes, managed with 15 units/day of insulin degludec, 50 mg/day of vildagliptin; hypertension losartan 50 mg/day, and chronic kidney disease grade II was treated at the nephrology clinic. She was referred to the dermatology department with a presumptive diagnosis of psoriasis.

Dermatological examination observed a disseminated dermatosis on the face, particularly on the chin (Figs. 1a and 1b), preauricular regions, nape, elbows (Figs. 2a and 2b), and the dorsum of the toes, characterized by scaly and crusted plaques. The remainder of the physical examination was normal.

	Figures 1: (a and b) Hyperkeratotic yellowish plaques and hemorrhagic crusts.
	Figures 2: (a and b) Hyperkeratotic plaques on the elbows, predominantly on the left.

The patient began experiencing symptoms six weeks previously, beginning with dryness in various parts of the body, especially on the face. She received treatment with unspecified creams yet decided to consult further. Her family and personal medical history was negative.

Based on these clinical findings, a diagnosis of Norwegian scabies was reached. The treating physician was instructed to perform a search for mites, which unfortunately could not be performed. Ivermectin was prescribed: 1 dose of 12 mg per week for two weeks, resulting in clinical resolution of the condition (Figs. 3a and 3b).

Figures 3: (a and b) Complete resolution two weeks after treatment.

Human scabies, particularly in its crusted form, presents a significant diagnostic and treatment challenge due to its atypical presentation and the large number of mites involved. Effective management requires a thorough understanding of its clinical manifestations and prompt treatment with ivermectin. Crusted scabies is especially prevalent among individuals with compromised immune systems, such as those with diabetes or HIV/AIDS, where impaired immune responses and peripheral neuropathy complicate diagnosis and treatment. Early detection, accurate diagnosis through microscopy or dermoscopy, and adherence to treatment guidelines are crucial for effective resolution, with a high success rate observed when appropriate treatment regimens are followed.

REFERENCES

1. Chandler DJ, Fuller LC. A review of scabies:An infestation more than skin deep. Dermatology. 2019;235:79-90.

2. Mauro A, Colonna C, Taranto S, Garella V, Castelletti F, Giordano L, et al. The hidden scabies:A rare case of atypical Norwegian scabies, case report and literature review. Ital J Pediatr. 2024;50:7.

3. Destra E, Andari Q, Harlim C, Nugraha H. View of Norwegian scabies in diabetic patient:A case report and literature review. Jurnal Medika Hutama. 2022;3:2519-24.

4. Bergamin G, Hudson J, Currie BJ, Mounsey KE. A systematic review of immunosuppressive risk factors and comorbidities associated with the development of crusted scabies. Int J Infect Dis. 2024;143:107036-45.

5. Lee K, Heresi G, Al Hammoud R. Norwegian scabies in a patient with down syndrome. J Pediatr. 2019;209:253-253.1.

6. Rahmawati NA, Chomariyati A, Mudjanarko SW. A fatal case of Norwegian scabies in a patient with diabetes mellitus. Bali Med J. 2022;11:870-4.

7. Richards RN. Scabies:Diagnostic and therapeutic update. J Cutan Med Surg. 2021;25:95-101.