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Hair Loss In Men:
Cause, Classification
& Diagnosis
by Bernstein Medical |
Dr.
Robert Bernstein
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The
Cause of Hair Loss in Men
By far the most common cause of hair loss in men is androgenetic
alopecia, also referred to as “male pattern alopecia” or “common
baldness.” It is caused by the effects of the male hormone
dihydrotestosterone (DHT) on genetically susceptible scalp hair
follicles.
This sensitivity to DHT is present mainly in hair follicles that
reside in the front, top, and crown of the scalp (rather than the back
and sides) producing a characteristic and easily identifiable pattern
described by Norwood (see Norwood Classification). Although it is
frequently stated that “hair loss comes from the mother,” the
condition can be inherited from either side of the family.
DHT is
formed by the action of the enzyme 5-alpha reductase on testosterone,
the hormone that causes sex characteristics in men. DHT causes male
hair loss by shortening the growth, or anagen, phase of the hair
cycle, causing miniaturization (decreased size) of the follicles, and
producing progressively shorter, finer hairs. Eventually these hairs
totally disappear.
In the patient below, we see a close-up of the side of his scalp where
the hair is not affected by DHT. We see mostly groups of full
thickness hairs (called terminal hairs) and a few scattered fine,
vellus hairs. This is normal.
In the
area of thinning (see circle below), we see that most of the hair has
been miniaturized, although all of the hair is still present.
In the
region that is bald (second circle in the center) , there is extensive
miniaturization and some, but not all of the hair has disappeared.
What
this shows is that the initial appearance of balding is due to the
progressive decrease in hair shaft size, rather than the actual loss
of hair – in early hair loss, all the hair is still present. This is
the reason why medications, such as finasteride (Propecia) work in
early hair loss (since they are able to partly reverse the
miniaturization process) but don’t work in areas that are totally
bald. It is also the reason why surgery, if not planned properly, can
result in hair loss due to the shedding of surrounding miniaturized
hair.
More about androgenetic hair loss:
Androgenetic hair loss is caused by three interdependent factors:
genes, hormones, and age:
• Genes
Common baldness cannot occur without the presence of specific
inherited genes. These genes can be passed on by either parent. A gene
is a single bit of chemically encoded hereditary instruction that is
located on a chromosome and actually represents a tiny segment of DNA.
Chromosomes occur in pairs (humans have 23 pairs), and every
individual gets one set of chromosomes from each parent. Hair loss in
men is now felt to involve more than one gene. When several genes
govern a trait, it is called polygenic.
Genes that are located on the X or Y-chromosomes are call sex-linked.
Genes on the other 22 pairs of chromosomes are called autosomal. It is
felt that the genes governing common baldness are autosomal (not sex
linked). This means that the baldness trait can be inherited from the
mother's side of the family or the father's side with equal frequency.
The commonly held notion that baldness comes only from the mother's
side of the family is incorrect, although for reasons not fully
understood, the predisposition inherited from an affected mother is of
slightly greater importance than that inherited from an affected
father.
The term, "dominant" means that only one gene of a pair is
needed for the trait to show up in the individual. A
"recessive" gene means that both genes need to be present in
order for the trait to be expressed. The genes involved in
androgenetic alopecia are felt to be dominant.
Just because one has the genes for baldness, it doesn't mean the trait
will manifest itself. The ability of a gene to affect one's
characteristics, i.e. be visible in a particular individual, is called
"expressivity". Gene expression is related to a number of
factors, the major ones being hormones and age, although stress and
other factors can play a role in some individuals.
It is of interest that, although genes for some types of male hair
loss have been mapped, none of the genes for male pattern baldness
have yet been identified. This suggests that any kind of genetic
engineering to prevent common baldness is still many years away.
• Hormones
Hormones are biochemical substances that are made in various glands
throughout the body. These glands secrete their products directly into
the bloodstream so that the chemical they make is spread throughout
the body. These chemicals are very powerful so that only minute
amounts of them have profound effects upon the body.
The major male sex hormone is called testosterone. Testosterone and
other related hormones that have masculinizing effects are made
primarily in the testicles; therefore, the hormonal levels that are
seen in adults do not reached significant levels until the testicles
develop and enlarge during puberty. In fact, these same hormones are
the cause of many of the changes that occur in puberty; growth of
phallus and scrotum, sperm production, development of a sex drive,
change in the voice, growth of axillary and pubic hair, development of
an adult aroma in the sweat, increase in bone and muscle mass, and
change in the basic body shape.
These same hormones that cause acne and beard growth can also signal
the beginning of baldness. The presence of androgens; testosterone,
and its related hormone DHT, cause some follicles to regress and die.
In addition to the testicles, the adrenal glands located above each of
our kidneys, produce androgenic hormones, and this would be similar in
both sexes. In females, the ovaries are an additional source of
hormones that can affect hair.
The specific relationship between testosterone and hormonally induced
hair loss in men was discovered by a psychiatrist early in this
century. At that time, castration was commonly performed on patients
with certain types of mental illness as it seemed to have a calming
effect upon many patients and castration reduced the sex drive of
patients who had no outlet for their desires. The doctor noted that
the identical twin brother of one patient was bald while the mentally
ill (castrated) twin had a full head of hair. The doctor decided to
determine the effect of treating his patient with testosterone, which
had recently become available in a purified form. He injected the
hairy twin with testosterone to see what would happen. Within weeks,
the hairy twin began to lose all but his wreath of permanent hair,
just like his normal twin. The doctor, then, stopped giving the
testosterone to see whether the process would be reversed, but the
balding process continued and his patient never regained his full head
of hair. It was apparent to him that eliminating testosterone will
slow, or stop, further hair loss once it has begun, but it will not
revive any dead follicles.
The hormone felt to be directly involved in androgenetic alopecia is
actually dihydrotestosterone (DHT) rather than testosterone. DHT is
formed by the action of the enzyme 5-a reductase on testosterone. DHT
acts by binding to special receptor sites on the cells of the hair
follicles to cause the specific changes associated with balding.
In men, 5-a reductase activity is higher in the balding area. This
helps to explain the reason for the patterned alopecia that males
experience. The enzyme 5-a reductase is inhibited by the hair loss
medication finasteride (Propecia).
DHT decreases the length of the anagen (growing) cycle, and increases
the telogen (resting) phase, so that with each new cycle the hair
shaft becomes progressively smaller. In addition, DHT causes the
bitemporal reshaping of hairline seen as adolescents enter adulthood,
as well as patterned baldness (androgenetic alopecia). DHT also causes
prostate enlargement in older men and adolescent and adult acne.
It is interesting that testosterone effects axillary and pubic hair,
whereas DHT effects beard growth, hair on trunk and limbs, patterned
baldness and the appearance of hair in the nose and ears (something
that older men experience). Scalp hair growth, however, is not
androgen dependent, only scalp hair loss depends on androgens.
• Age
The presence of the necessary genes and hormones are not alone
sufficient to cause baldness. Even after a person has reached puberty,
susceptible hair follicles must continually be exposed to the hormone
over a period of time for hair loss to occur. The age at which these
effects finally manifest themselves varies from one individual to
another and is related to a person's genetic composition and to the
levels of testosterone in the bloodstream.
There is another time factor that is poorly understood. Male hair loss
does not occur all at once nor in a steady, straight-line progression.
Hair loss is characteristically cyclical. People who are losing their
hair experience alternating periods of slow and rapid hair loss and
even stability. Many of the factors that cause the rate of loss to
speed up or slow down are unknown, but we do know that with age, a
person's total hair volume will decrease.
Even when there is no predisposition to genetic balding, as a patient
ages, some hairs randomly begin to miniaturize (shrink in length and
width) in each follicular unit. As a result, each group will contain
both of full terminal hairs and miniaturized hairs (similar to the
very fine hairs that occur on the rest of the body and are clinically
insignificant) making the area look less full. Eventually, the
miniaturized hairs are lost, and the actual follicular units are
reduced in number. In all adult patients, the entire scalp undergoes
this aging process so that even the donor zone is not truly permanent,
but will gradually thin, to some degree, over time. Fortunately, in
most people, the donor zone retains enough permanent hair that hair
transplantation is a viable procedure even for a patient well into his
70's
The
Classification of Hair Loss in Men
Norwood Classification
The Norwood classification, published in 1975 by Dr. O’tar Norwood,
is the most widely used classification for hair loss in men. It
defines two major patterns and several less common types (see the
chart below). In the regular Norwood pattern, two areas of hair
loss--a bitemporal recession and thinning crown--gradually enlarge and
coalesce until the entire front, top and crown (vertex) of the scalp
are bald.
Class I
represents an adolescent or juvenile hairline and it not actually
balding. The adolescent hairline generally rests on the upper brow
crease.
Class II indicates a progression to the adult or mature hairline which
sits a finger breath (1.5cm) above the upper brow crease, with some
temporal recession. This also does not represent balding.
Class III is the earliest stage of male hair loss. It is characterized
by a deepening temporal recession.
Class III Vertex represents early hair loss in the crown (vertex).
Class IV Is characterized by further frontal hair loss and enlargement
of vertex, but there is still a solid band of hair across top
separating front and vertex.
Class V the bald areas in the front and crown continue to enlarge and
the bridge of hair separating the two areas begins to break down.
Left:
Typical Norwood Class V showing two distinct areas of hair loss with
the bridge of hair separating the front and back thinning
significantly.
Right: Class VI showing the confluence of the front a back to form one
bald area.
Class VI occurs when the connecting bridge of hair disappears leaving
a single large bald area on the front and top of the scalp. The hair
on the sides of the scalp remains relatively high.
Class VII patients have extensive hair loss with only a wreath of hair
remaining in the back and sides of the scalp.
Norwood Class A
The Norwood Class A patterns are characterized by a front to back
progression of hair loss. Norwood Class A’s lack the connecting
bridge across the top of the scalp and generally have more limited
hair loss in the crown, even when advanced.
The
Norwood Class A patterns are less common than the regular pattern
(<10%), but are significant because of the fact that, since the
hair loss is most dramatic in the front, the patients look very bald
even when the hair loss is minimal. Men with Class A hair loss often
seek surgical hair restoration early, as the frontal bald area is not
generally responsive to medication and the dense donor area contrasts
and accentuates the baldness on top. Fortunately, Class A patients are
excellent candidates for hair transplantation.
Left:
Norwood Class IVa with anticipated hairline drawn. Right: Early Class
Va with some residual hair on the top of the scalp. Note that in both
stages there is a complete absence of hair in the front part of the
scalp.
In both Norwood patterns, the sides and back tend to resist
androgenetic changes, although the sides may exhibit significant
thinning in old age (senile alopecia.)
Diffuse Patterned and Unpatterned Alopecia
Two other types of genetic hair loss in men not often considered by
doctors, “Diffuse Patterned Alopecia” and “Diffuse Unpatterned
Alopecia,” pose a significant challenge both in diagnosis and in
patient management. Understanding these conditions is crucial to the
evaluation of hair loss in both men and women, particularly those that
are young when the diagnoses may be easily missed, as they may
indicate that a patient is not a candidate for surgery. (Bernstein and
Rassman “Follicular Transplantation: Patient Evaluation and Surgical
Planning”)
Diffuse Patterned Alopecia (DPA) is an androgenetic alopecia
manifested as diffuse thinning in the front, top and crown, with a
stable permanent zone. In DPA, the entire top of the scalp gradually
miniaturizes (thins) without passing through the typical Norwood
stages. Diffuse Unpatterned Alopecia (DUPA) is also androgenetic, but
lacks a stable permanent zone and affects men much less often than DPA.
DUPA tends to advance faster than DPA and end up in a horseshoe
pattern resembling the Norwood class VII. However, unlike the Norwood
VII, the DUPA horseshoe can look almost transparent due to the low
density of the back and sides. Differentiating between DPA and DUPA is
very important because DPA patients often make good transplant
candidates, whereas DUPA patients almost never do, as they eventually
have extensive hair loss without a stable zone for harvesting.
The
progression of male hair loss in Diffuse Patterned Alopecia (DPA) and
Diffuse Unpatterned Alopecia (DUPA). In DUPA, the sides thin
significantly as well.
The
Diagnosis of Hair Loss in Men
The diagnosis of androgenetic alopecia in men is generally
straightforward. It is made by observing a “patterned”
distribution of hair loss (see the previous session on Classification)
and confirmed by observing the presence of miniaturized hair in the
areas of thinning.
Miniaturization – the progressive decrease of the hair shaft’s
diameter and length in response to androgens – can be observed using
a densitometer, a hand-held instrument that magnifies a small area of
the scalp where the hair has been clipped to about 1mm in length.
Hair
Densitometer
The photo, below left, was taken from a normal scalp. The follicular
units (groups) are made of predominately of full-thickness, healthy
terminal hair. Note the relatively uniform diameter of the hair
shafts. The photo, below right, shows that many hairs have decreased
in diameter (miniaturized). This is characteristic of androgenetic
alopecia.
The
diagnosis of androgenetic alopecia is supported by a family history of
hair loss, although a positive history is not always identified. (see
Genetics) In older patients, their own history of passing through the
different Norwood stages is strongly suggestive of male pattern
alopecia.
If the hair loss is diffuse (thin all over) rather than following one
of the specific Norwood patterns, the diagnosis can be more difficult.
However, the presence of miniaturization in the areas of thinning
usually confirms the diagnosis of androgenetic alopecia. If the
diagnosis is still unclear, a number of other conditions must be ruled
out.
Medical conditions that can produce diffuse hair loss in men include
thyroid disease and anemia. Certain medications, including some drugs
used for high blood pressure and depression, and the use of anabolic
steroids, can also cause male hair loss.
The following laboratory tests are often useful when a non-androgenetic
cause for diffuse hair loss is suspected: blood chemistries, complete
blood count, serum iron, thyroid functions, and tests for lupus and
syphilis.
When the diagnosis of androgenetic alopecia is still uncertain,
further diagnostic information can be obtained from a hair-pull test,
a scraping and culture for fungus, a microscopic examination of the
hair bulb and shaft, and a scalp biopsy. A dermatologic consultation
is warranted whenever the cause of hair loss is unclear.
The
above is contributed by Bernstein Medical
125 East 63rd Street, New York, New York 10021 212-826-2400
2150 Center Ave., Fort Lee, New Jersey 07024 201-585-1115
Toll Free: 1-866-576-2400 contact@bernsteinmedical.com
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