Page 217 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 7-6 Hair and Nail Diseases

HAIR SHAFT ABNORMALITIES

There are a wide variety of hair shaft abnormalities.
Most are nonspecific clinical findings that can be seen
in a multitude of underlying conditions, as well as in
the normal individual. Trichoptilosis, known by the lay
term “split ends,” is probably the most common hair
shaft abnormality in humans. It is nonspecific and is not Pili torti
associated with any particular underlying syndrome.
Trichoptilosis is believed to be caused by excessive
trauma to the distal hair shaft. Trichorrhexis nodosa is Trichorrhexis nodosa
another hair shaft abnormality that can be seen in indi-
viduals with no underlying disease state. A few highly
specific hair abnormalities are indicative of particular
disorders; for example, pili trianguli et canaliculi and
trichorrhexis invaginata are seen only in uncombable
hair syndrome and Netherton syndrome, respectively.
The astute clinician uses knowledge of hair shaft abnor-
malities to help form a differential diagnosis and in
some cases to confirm a diagnosis.
Pili torti is also known as “twisted hair” or “cork-
screw hair.” The hair twists on its axis in a corkscrew
pattern. This twisting leads to increased pressure on the
hair shaft, which results in early breakage and short,
brittle hair. The involvement is almost exclusively on
the scalp. Pili torti is nonspecific and can be found in a
number of genetic skin conditions, including Björnstad
syndrome, Menkes syndrome, and Crandall syndrome.
It can also be seen as a primary hair disease with no
underlying associations.
Monilethrix is a highly specific hair shaft abnormal-
ity. The hair has a beaded or undulating appearance,
with nodes interspaced at regular intervals by abnor- Pili trianguli et canaliculi
mally thin hair. It is inherited in an autosomal dominant
fashion and is caused by a mutation in the hair basic
keratin 6 gene (HB6), which is officially known as
keratin 86 (KRT86). The hair is fragile and breaks in the
thinned internode regions. The internode regions are
devoid of pigment, and this feature is used to discrimi-
nate this condition from pseudo-monilethrix. There is
no known therapy. Many afflicted individuals improve Monilethrix
after puberty. It is almost never associated with systemic
disease.
Trichorrhexis nodosa is a completely nonspecific
finding that may be seen in healthy individuals. This
hair shaft abnormality has been described as “broom-
stick hair” because of the appearance of the distal end
of the broken hair, which resembles the bristles of a
broom. Trichorrhexis nodosa is the most frequent
reason for hair breakage. Trauma to the hair is caus-
ative. This trauma can be self-induced by rubbing or
twisting, which results in fracturing of the hair and the
appearance of trichorrhexis nodosa. This finding on
microscopic examination can be helpful in evaluating
hair loss secondary to trichotillomania or chemical-
induced alopecia. Trichorrhexis invaginata
Pili trianguli et canaliculus, also termed “spun glass
hair,” is the diagnostic finding in uncombable hair syn-
drome. This rare and highly unusual syndrome is asso-
ciated with no underlying ill effects on the afflicted
individuals. The hair is uncontrollable and impossible
to comb straight. This effect is related to the abnormal Trichorrhexis invaginata is seen only in patients with invaginata. Netherton syndrome is a multisystem
triangular shape of the hair shaft as well as changes in the autosomal recessive Netherton syndrome. This hair disease caused by a mutation in the SPINK5 gene that is
the direction of the hair, which occur at uneven inter- shaft abnormality has been termed “bamboo hair” associated with erythroderma, alopecia, and elevated
vals. The condition is inherited in an autosomal domi- because of its resemblance to the growth rings of a levels of immunoglobulin E. Ichthyosis linearis circum-
nant pattern and is believed to be the result of an bamboo plant. Another descriptive term is “ball and flexa is the name for the migratory, irregular, serpigi-
abnormal inner root sheath. No therapy is needed, and socket hair,” because it appears that the distal portion of nous patches and plaques with a double-edged scale that
most children with this condition spontaneously the hair invaginates into the proximal hair cortex. The are seen only in Netherton syndrome. The SPINK5
improve over time. The hair shafts appear almost tri- hair is brittle and breaks easily, leading to alopecia. The gene encodes the serine protease inhibitor, Kazal type 5
angular under electron microscopy. eyebrow hair is the best place to look for trichorrhexis protein, which is important in epithelial desquamation.

THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS 203