is a viral skin infection, caused
by the molluscum contagiosum virus, a member of the
poxvirus family. The disease is characterized by ﬂ
colored, dome-shaped, pearly papules with a dimpled
center. Lesions are typically 1 to 5 mm in diameter
and common on the trunk, arms, and legs. The disease
is common in childhood, and usually self-limited in
immunocompetent patients. In adults, the disease usu-
ally indicates cellular immunodeF
ciency. The papules
are usually nonpainful, but may itch or be complicated
by secondary infection. The diagnosis is mainly based
on the clinical appearance of the lesions. This slide
shows lobules of keratinocytes with large eosinophilic
intracytoplasmic inclusions called
within the stratum granulosum and stratum corneum.
The treatment may include laser therapies, cryotherapy,
or curettage, or there may be no treatment at all.
is a translucent, hard, keratinized
sheet resting on the tip of each digit. It includes
many components: (1) the
, the nail
itself, which is hard keratin; (2) the
also called the
, seen as the
in the living state; (3) the
, a layer of
epidermis beneath the nail plate; (4) the
, also called the
, which is the
junction zone between the skin of the F
and the nail plate and which forms a protec-
tive seal; (5) the
skin that surrounds the edge of the nail; and
, the junction seal between
the nail plate and the skin of the F ngertip. All
of the sealed areas at the edges of the nail plate
protect the delicate nail matrix and nail bed
from dehydration and infection.
Nail root (matrix) and nail bed.
is a cellular layer and is also called the
. It contains many layers of epithelial cells, which
are responsible for the production of the
. These cells
proliferate and become ﬂ
attened and highly keratinized and are
pushed forward by newly formed cells. As they differentiate, the
nally lose color and shape and become part of the nail plate.
The nail plate is similar to the hair shaft, but the pattern of kera-
tin formation is different. The nail bed (equivalent to the epider-
mis) rests under the nail plate. The nail bed extends from the nail
matrix to the hyponychium.
is smooth and allows for healthy nail
growth and a smooth appearance. If a nail bed is infected by
, the nail bed becomes rough, and an accumu-
lation of organic waste materials can react with the nail plate
and cause the nail to become thickened and distorted.