fungal infection of scalp

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This is a fungal infection of scalp hair follicles and the surrounding skin, caused by dermatophyte fungi, usually by species in the genera Microsporum and Trichophyton.

  • in some patients, there is a pronounced inflammatory reaction, a feature often seen in zoophilic infections or those spread from animals to human; by contrast in others, particularly those with anthropophilic dermatophytosis spread from human to human, lesions are often non-inflammatory and persistent
  • principal changes in the epidemiology of tinea capitis in recent years has been the rise of Microsporum. canis as the dominant organism in infections in some parts of Europe and the spread of T. tonsurans in urban communities in the USA and Western Europe, e.g. the UK and France

  • according to the host preference and natural habitat, dermatophytes can be classified into
    • anthropophilic e.g - Trichophyton tonsurans, Microsporum audouinii
      • most frequently incurred by contact with an infected child, either directly or via fomites
      • in children with continued reinfection, consider an asymptomatic adult carrier

    • zoophilic e.g. - Microsporum canis
      • stray cats and dogs as well as pet puppies, kittens and rabbits are the most important dermatophyte carriers
    • geophilic (1)

  • Microsporum canis  is the predominant causative agent across Europe and worldwide
    • an emerging number of anthropophilic scalp infections has been reported in the UK e.g. - Trichophyton tonsurans was responsible for 50–90% of dermatophyte scalp isolates
      • this increase is attributed to immigration and travel patterns (1,2).

It occurs almost exclusively in pre-pubertal children. Infants are less frequently affected. The incidence in adults is generally low, but it is more commonly seen in the immune compromised, where the presentation may be atypical

  • prevalence in Europe ranges between 0.23% and 2.6%
  • in the UK, it is common in inner-city cosmopolitan communities (1,2,3)
  • n the United States, tinea capitis most commonly affects children of African heritage between three and nine years of age (4)

According to the type of hair invasion, dermatophytes can be classified as:

  • endothirx
    • the fungus is located within the hair shaft 
    • the hyphae are converted to arthroconidia (spores) within the hair
    • the cuticle surface of the hair remains intact
  • ectothirx
    • fungus is present around the exterior of the hair shaft
    • arthroconidia may develop both within and outside the hair shaft (1)

Complications

  • secondary bacterial infection is not common even in kerion, where this may occur under large superficial crusts rather than in the form of folliculitis
  • a phenomenon sometimes seen with inflammatory tinea capitis such as kerion is the emergence of a secondary rash, usually small follicular papules in other areas of the body such as the trunk or limbs
    • erythema nodosum has been described as a rare association with tinea capitis
    • these reactions are known as id reactions - thought to represent an immune complex deposition reaction (5)

 Reference:

Last edited 01/2019 and last reviewed 10/2020

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