What is alopecia areata?
Alopecia areata is a patchy hair loss that is usually of sudden onset and can arise on any hairy part of the body. It is a non-scarring type of hair loss with no obvious skin disease or lesion or other underlying systemic disturbance. Most cases involve the scalp or beard and rarely it can all of the body where it is known as alopecia universalis. Complete loss of scalp hair is known as alopecia totalis, or more specifically as alopecia capitis totalis.
Alopecia areata must be differentiated from the two most common types of hair loss – androgenetic alopecia and telogen effluvium – where hair loss is generally diffuse. With androgenetic alopecia, the hair loss typically follows a pattern of a receding hairline and/or loss at the crown which is described as male-pattern or female-pattern hair loss. In telogen effluvium, the hair is shed gradually over a period of time and gives the appearance of thinning hair without any complete balding. Alopecia areata presents as complete hair loss in patches that can expand or coalesce to form patterns similar to androgenetic alopecia and telogen effluvium.
Why does alopecia areata occur?
The exact cause of alopecia areata is not known but there are several theories as to why it occurs. The most popular of these is that it is due to autoimmune factors. Normally the immune system forms antibodies as a means of “tagging” foreign pathogens. These antibodies are produced in response to the proteins on the pathogens and when it binds to it, immune cells can then target these invaders.
The same process appears to occur in alopecia areata with antibodies formed against the hair follicles. Once attached, the immune cells are directed to act against the follicles. Most of the time the action is directed at the outer root sheath but can also affect the inner parts of the follicles. It appears that the antibodies are more often formed against hair follicles in the anagen phase. This is the period of active growth and if disrupted, no growth will occur in the transitionary catagen phase or resting telogen phase of hair growth.
Types of Alopecia Areata
Alopecia areata can be classified according to the pattern of hair loss. This can sometimes mimic telogen effluvium and androgenetic alopecia (male- / female-pattern baldness).
- Patchy alopecia areata is small isolated spots of hair loss involving less than 50% of the site.
- Reticular-pattern alopecia areata also presents as patches, but usually involves more than 50% of the site with these patches often coalescing.
- Ophiasis-pattern alopecia areata is localized hair loss that tends to occur on the back of the scalp (occipital) and sides (temporal).
- Sisaipho-pattern alopecia areata involves other areas of the scalp but spares the sides and back of the scalp. This is sometimes mistaken for male-pattern baldness (androgenetic alopecia).
- Alopecia totalis is complete balding involving the entire scalp.
- Alopecia universalis is complete hair loss on all the hairy parts of the body.
Causes of Alopecia Areata
Although the autoimmune theory is more widely accepted as the underlying mechanism in alopecia areata, it is believed that other factors may contribute to it or act as triggers. Genetic susceptibility is the only known risk factor and the autoimmune disturbance is therefore inherited. However, other contributing factors that have not as yet clearly been identified as risk factors may also play a role. This includes :
- Other autoimmune disorders, like thyroiditis, myasthenia gravis and vitiligo.
- Atopic dermatitis and a history of atopy, which may include allergic asthma and allergic rhinitis.
- Down syndrome
- Diabetes mellitus
- Psychiatric conditions ranging from depression and other mood disorders to personality and paranoid disorders. Compulsive hair pulling (trichotillomania) needs to be identified in these scenarios.
- Emotional stress associated with grief and anxiety.
It appears that alopecia areata may be associated with several of the risk factors seen with telogen effluvium as discussed under causes of shedding hair. These predisposing factors may include :
- Febrile illnesses
- Major surgery
- Certain drugs
- Viral infections
Alopecia Areata and HIV
Hair loss in HIV is not uncommon and reported by many HIV/AIDS patients. Most cases appear to be patchy hair loss (alopecia areata) although patients report a generalized shedding of the hair (telogen effluvium). It tends to be more frequently seen in patients on HAART (highly active antiretroviral therapy), particularly in patients using agents such as indinavir.
Individuals with short hair may notice loss at the rear hairline (occipital hairline) which is not receding but rather patches of complete hair loss as is seen with the ophiasis pattern. However, this pattern is not typical for alopecia areata in HIV and can affect any part of the scalp. The role of opportunistic infections, nutritional deficiencies, depression and endocrine dysfuction related to HIV needs to be investigated as possible causes of the hair loss rather than just the infection itself or its effects on immune function.
Signs and Symptoms
The clinical presentation of alopecia areata varies among individuals. The patches of balding is typically round or oval in shape. The skin appears smooth and sometimes slightly red but is not associated with a rash. Most patients experience a single patch of hair loss although multiple patches may be seen. The scalp and beard are the most common sites and less frequently seen sites include the eyebrows, arms or legs.
As with most non-scarring types of alopecia, there is usually no other signs or symptoms although a minority of patients may report some itching at the site or a burning sensation. In these cases, allergic contact dermatitis needs to be investigated. Involvement at a specific site like the scalp or beard can be classified as localized where there is less than 50% involvement or extensive where there is more than 50% involvement. Localized involvement is more common. More than one site may be affected simultaneously.
Other clinical features that may accompany alopecia areata include distortions of the nails. Trachyonychia which is a fine roughness and white discoloration of the nails may be seen with severe forms of alopecia areata. This is also known as twenty-nail dystrophy because it tends to affect all the nails, both on the fingers and toes. This is discussed further under rough nails. Other form of nail distortions may include pitting, spoon-shaped (koilonychia) and Beau’s lines (particularly after severe illness) and may be more likely to affect the fingernails. Read more fingernail ridges.
Pictures of Alopecia Areata
Source : Dermatology Atlas (Courtesy Samuel Freire da Silva, M.D.)