Hair loss disorders are a large, heterogeneous group of conditions that have various clinical features, pathological findings, and etiologies. Hair loss may occur due to disorders of hair cycling, inflammatory conditions that damage hair follicles, or inherited or acquired abnormalities in hair shafts.
The major dividing line for the various forms of hair loss is the distinction among cicatricial (scarring) alopecia, non-scarring alopecia, and structural hair disorders.
Scarring Vs. Non-Scarring Alopecia
Cicatricial alopecias are conditions that lead to the irreversible cessation of hair cycling and permanent hair loss. The loss of hair follicle stem cells in the bulge region of the hair follicle is thought to contribute to the development of cicatricial alopecia.
In nonscarring alopecias, the hair follicle is not permanently damaged, making spontaneous or treatment-induced regrowth a possibility. Structural hair disorders that lead to hair loss demonstrate abnormalities within the hair shafts that result in hair fragility.
The primary cicatricial alopecias are inflammatory disorders of the scalp that lead to permanent hair loss. The primary cicatricial alopecias are subdivided by the type of inflammation detected on histologic examination from a scalp biopsy.
In non-scarring alopecias, clinical signs of inflammation are usually mild or absent, and destruction of the hair follicle does not occur. The definitive diagnosis of this disorder is also made by a scalp biopsy and histologic exam under the microscope.
These non-scarring alopecias are divided into three subgroups. There can be focal hair loss, such as alopecia areata, pressure induced alopecia, or traction alopecia, just to name a few. There can be patterned hair loss of which androgenetic alopecia in men, female pattern hair loss, and trichotillomania are the classic examples. Finally, there can be diffuse hair loss. In this group, there are several examples like anagen effluvium, loose anagen syndrome, and telogen effluvium to name a few.
Structural Hair Disorders
Structural hair abnormalities that result in brittle or fragile hair can lead to breakage or the appearance of a failure of hair to grow. Hair fragility may result from abnormal hair formation or external insults that damage the hair shaft.
The most common structural hair abnormalities are acquired trichorrhexis nodosa and trichoptilosis, both of which may occur as a result of harmful hair care practices, such as chemical processing, excessive brushing or teasing of hair, or the application of excessive heat. Trichorrhexis nodosa is characterized by disruption of the protective cuticle and fraying of the hair shaft. Trichoptilosis is a term that describes splitting and fraying of the distal end of the hair shaft, which is commonly referred to as “split ends.” Bubble hair, where there are bubble-like structures within the hair shaft, is another microscopic finding that may be seen in heat-damaged hair.
Various forms of hair loss may masquerade as other forms of hair loss. This is why it is important to know the cause of the alopecia in order to achieve the best treatment outcome.
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