Dysfunctions of Melanocytes
There are three significant dysfunctions of mela-
nocytes:
•ALBINISMis a deficit or absence of pigmentation
(hypopigmentation) caused by a MUTATION in
the genetic encoding for tyrosinase. The body
may produce little or none of this enzyme,
reducing or completely blocking melanogene-
sis. The dermatologic consequence is extremely
light-colored skin that cannot protect itself
from ultraviolet light damage.
•VITILIGO is a hypopigmentation disorder of
autoimmune origin in which the melanocytes
in areas of the skin die, leaving the skin with-
out pigmentation.
- Malignant melanoma is a serious type of SKIN
CANCERthat arises from melanocytes.
For further discussion of melanocytes within
the context of integumentary structure and func-
tion, please see the overview section, “The Integu-
mentary System”.
See also AMINO ACIDS; KERATINOCYTE; PHENYLKE-
TONURIA(PKU).
melasma See CHLOASMA.
miliaria Small bumps that form on the SKINin
environmental conditions of high heat and
humidity, when the body produces much sweat
that cannot evaporate and instead pools on the
surface of the skin. The bumps may be red (mil-
iaria rubra) or clear and filled with fluid (miliaria
crystallina). Clothing may further inhibit sweat
evaporation. The pooling creates irritation and
INFLAMMATION that obstructs the sweat glands.
Most miliaria, commonly called heat RASH,
improves with self-care to cool the body, which
causes the SWEAT GLANDSto decrease production.
The skin bumps generally go away in three to five
days. Newborns are particularly susceptible to
miliaria in the first week or two of life. Miliaria
also sometimes occurs in people who have high
fevers.
See also HEAT EXHAUSTION; HEAT STROKE; HYPER-
THERMIA.
Mohs’ micrographic surgery A specialized tech-
nique for removing certain skin cancers such as
basal cell carcinomas and squamous cell carcino-
mas. In an outpatient OPERATION(AMBULATORY SUR-
GERY) with local anesthetic and a sedative for
relaxation if necessary, the dermatologist removes
one thin layer of the tumor at a time and exam-
ines each specially stained layer under the micro-
scope. The surgery continues until the tissue
sample shows a one- to two-millimeter margin of
healthy tissue on all borders, ensuring that the
dermatologist removes all of the malignancy.
Because Mohs’ micrographic surgery is so precise
it removes only the malignancy, sparing as much
surrounding tissue as possible.
By comparison, conventional excision removes
the tumor and what the surgeon believes is a rea-
sonable amount of surrounding tissue to provide
clean margins, which can result in removing con-
siderably more tissue than just the malignancy. A
pathologist later examines frozen sections of the
tissue to confirm the margins. With conventional
excision there is a change that the margins could
be positive (contain cancer cells) and the surgeon
would have to do another operation to remove
more tissue.
Dermatologists use Mohs’ micrographic surgery
when the SKIN CANCERis on the face, nose, eyelids,
or around the mouth, or if it is a larger, more
aggressive cancer on the body. The procedure may
take several hours altogether to complete,
depending on how many layers of tissue the der-
matologist must remove to get clean margins.
Many cancers removed using Mohs’ micrographic
surgery heal with minimal scarring. The dermatol-
ogist performing the surgery usually repairs any
residual defect as dermatologists also perform
reconstructive surgery. Mohs’ micrographic sur-
gery has an overall cure rate of 95 percent and up
to 99 percent for certain kinds of malignant
lesions, the highest for all current forms of treat-
ment for these two types of skin cancer. Frederic
E. Mohs, M.D. (1910–2002), discovered the tech-
nique while a medical student in the 1930s.
See also CANCER TREATMENT OPTIONS AND DECI-
SIONS; LESION; SURGERY BENEFIT AND RISK ASSESSMENT.mole See NEVUS.176 The Integumentary System