Pruritus of the scalp is a common symptom in everyday dermatology. The spectrum of possible causes is very broad. Vázquez-Herrera et al. have identified the six most common causes based on a secondary analysis, which they summarize under the acronym “SCALLP”. If none of these diagnoses apply, the fan must be opened. It can be caused by one or more of a variety of dermatological or systemic diseases.
Like pruritus in general, itching on the scalp can be due to both dermatoses and non-dermatological diseases. In order to systematize the search for causes, Vázquez-Herrera et al. conducted a Pubmed search including clinical studies, reviews, case series and case reports from the period 1975-2017 [1]. As a result, these are the most common causes of scalp itching (acronym “SCALLP”):
- Seborrheic dermatitis (seborrheicdermatitis)
- Contact dermatitis (Contactdermatitis)
- Anxiety disorders (Anxiety)
- Lichen planopilaris (Lichenplanopilaris)
- Lice (Lice)
- Psoriasis (psoriasis).
Dermatoscopy/trichoscopy, biopsy and smear tests have proven effective for diagnostic clarification. Histopathology is particularly informative in cases of doubt.
Seborrheic dermatitis: Trichoscopy shows branched vessels in seborrheic dermatitis and contact dermatitis, while in psoriasis red dots can be seen at low magnification and twisted capillary loops at high magnification [2].
Contact dermatitis: Arborizing vessels are often seen on trichoscopy. Contact dermatitis is often a complication of other scalp diseases, as a disturbed skin barrier leads to sensitization.
Microbial infestation: In some patients with scalp itching, lice, scabies or other microbes are the triggers. Although scabies does not usually occur on the scalp in immunocompetent adults, it does occur in immunocompromised patients and children [3].
Psoriasis: In trichoscopy, red dots and scabs can be seen in up to 87% of patients at tenfold magnification [4]. At higher magnification, twisted loops are characteristic; glomerular vessels may also be present [5].
In addition to these, the authors also discuss the following dermatological differential diagnoses in more detail [1]:
- Tinea capitis
- Urticarial lesions
- atopic dermatitis
- Dermatomyositis
- Extrafacial rosacea (“red scalp syndrome”)
- Cicatricial alopecia
Other skin lesions (seborrheic keratosis, keloid scars, burns, eosinophilic, polymorphic and pruritic eruptions associated with radiotherapy)
With regard to systemic diseases, which can manifest themselves in the form of itchy scalp, according to Vázquez-Herrera et al. The following should be given priority [1]: metabolic diseases, hepatobiliary causes, paraneoplastic diseases, solid tumors, hematological causes, infectious diseases, iatrogenic causes, pregnancy.
The treatment of itchy scalp is based on the symptoms and the underlying disease and is ideally carried out as part of an individualized approach [6].
Literature:
- Vázquez-Herrera NE, et al: Scalp Itch: A Systematic Review. Skin Appendage Disord 2018; 4(3): 187-199.
- Tosti A. ed 2. Boca Raton: CRC Press; 2015. Dermoscopy of the Hair and Nails.
- Lewis EJ, et al: Localized crusted scabies of the scalp and feet. Cutis 1998; 61: 87-88.
- Haliasos EC, et al: Dermoscopy for the pediatric dermatologist part I: dermoscopy of pediatric infectious and inflammatory skin lesions and hair disorders. Pediatr Dermatol 2013; 30: 163-171.
- Miteva M, Tosti A: Hair and scalp dermatoscopy. J Am Acad Dermatol 2012; 67: 1040-1048.
- Rattanakaemakorn P, Suchonwanit P: Scalp Pruritus: Review of the Pathogenesis, Diagnosis, and Management. Biomed Res Int 2019 Jan 15; 2019: 1268430.
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