Alopecia overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Ogechukwu Hannah Nnabude, MD

Overview

Alopecia is defined as the loss of hair regardless of the cause. It can occur anywhere on the body. The hair cycle consists of three phases: the anagen phase, which is the growth phase, the catagen phase, which is the resting phase, and the telogen phase, which is the shedding phase. This is the phase where hair falls out. Ninety percent of hair is in the anagen phase and the remaining ten percent are in the catagen and telogen phases. In the telogen phase, hair is going to recycle, and it starts growing again in the anagen phase.

Historical Perspectives

The use of the word alopecia stretches back to the era of the Greek physician Hippocrates. Minoxidil and finasteride are the only FDA approved medications for treating alopecia. Hair transplant surgery originated in the 1900s and some of the major advancements in hair transplantation took place in Japan in the 1930s.

Classification

Alopecia is classified as either scarring or non-scarring. Over all, non-scarring alopecias tend to have better outcomes than scarring alopecias, which tend to be irreversible. The most common type is androgenetic alopecia. The majority of men start to lose hair in the third decade of life, while women begin to lose their hair in the fifth or sixth decade of life. As an individual ages, they will lose hair. Men more often lose hair in the front and the temporal regions of the scalp, while women tend to lose hair from the central area of the scalp. Also, female hair loss rarely results in complete baldness while male hair loss can end up with complete baldness. Males tend to retain hair at the posterior area of the scalp because the hair in this region is more resistant to the effects of androgenic hormones.

Pathophysiology

There are several pathophysiologic mechanisms responsible for alopecia, each related to the specific cause. For example, alopecia areata, is related with CD8+ T-cell autoimmunity, while androgenetic alopecia is related to the effects of androgen hormones hair follicles.

Causes

Scarring alopecia is caused by numerous dermatologic factors, including glabrous skin (non-hairy), and is very difficult to diagnose and manage. Non-scarring alopecia is characterized by the absence of visible inflammation of the skin involved. Medications, endocrine diseases, infectious diseases, and autoimmune diseases can also cause hair loss.

Differentiating Alopecia From Other Diseases

There is a very wide list of diseases and conditions that can lead to alopecia. Proper history taking and physical examination, along with laboratory, microbiology, and in some cases, imaging studies, are helpful in narrowing down the diagnosis.

Epidemiology and Demographics

The epidemiology and demographics of alopecia varies by age, race, sex, and health status. Androgenetic alopecia is the most common cause of alopecia. Traction alopecia is seen most often in black populations and is associated with tight hair braids. Tinea capitis commonly seen in the pediatric population. Trichotillomania is more common in males among younger patients and females among adults.

Risk Factors

There are multiple risk factors for alopecia including family history, medications, sex, age and illness. Androgenetic alopecia is more common in males and prevalence increases with age. People with a family history of hair loss are at greater predisposition to developing alopecia. Psychosocial stress, hormonal imbalance, and illness also increase the risk of alopecia.

Natural History, Complications and Prognosis

The progression and severity of alopecia is based on the cause. Patients with alopecia are at increased risk of psychosocial complications such as anxiety and depression. In addition, these patients need to be evaluated for other medical conditions. Outcomes vary with the type of alopecia. Non-scarring alopecias such as androgenetic alopecia, anagen effluvium and early tinea capitis may be reversible while scarring alopecias such as traction alopecia and favus may not be reversible.

Diagnosis

Biopsy, laboratory tests, trichoscopy, and hair pull test are some of the techniques used in diagnosis. Chest X-ray, CT scan and MRI can be used in mycosis fungoides staging and is useful for alopecia mucinosa while microscopic testing and Wood's lamp is useful for the diagnosis of fungal infection.