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Dermatofibromas (fibrous histiocytomas) are
red-to-brown, firm nodules, ranging in diameter from a few millimeters
to 2 centimeters. These benign lesions are often located on the
lower extremities and tend to persist indefinitely. Lateral pressure
on the lesion produces dimpling of its surface.1 Larger
lesions may be concerning for dermatofibrosarcomaprotuberans,
which is a rare, more invasive lesion. Biopsy is diagnostic in both cases
and may be necessary to distinguish the lesions. Biopsy of a dermatofibroma
reveals prominent fibrocytes and coarse bundles of collagen in a
haphazard fashion, frequently arranged in short fascicles that interweave
(“storiform pattern”). There is often hyperplasia
and hyperpigmentation of the overlying epidermis.2Dermatofibrosarcoma
protuberans is usually located on the trunk, often has
a blue hue, and may be mistaken for a vascular lesion.3 It
is locally invasive and may only rarely metastasize. Wide local
excision or Mohs surgery is indicated, and preoperative MRI may help
delineate the extent of the lesion before surgery.4
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Mastocytosis is a group of disorders in which increased
numbers of mast cells infiltrate tissues and organs, especially
the skin. Symptoms result from degranulation of mast cells. In contrast
to adult forms of the disease, mastocytosis in children often spontaneously
resolves. In the most common form of cutaneous mastocytosis, urticaria
pigmentosa, a varying number of brown-to-orange macules,
papules, or plaques cause a cobblestone or orange peel–like
appearance over any part of the skin surface (Fig.
363-1). Spontaneous wheals, vesicles, or paroxysms of pruritus
are not uncommon. The solitary mastocytoma presents
as a single orange-brown nodule or plaque that may also urticate
and blister with trauma, although severe pruritus is uncommon. Diffuse
cutaneous mastocytosis is a rare, severe form in which there
is marked and widespread infiltration of the skin with mast cells.
The skin is thickened, often with a yellow-orange hue, and widespread
blistering is often present. Bone, liver, spleen, gastrointestinal
tract, and other organs may also be involved. Extracutaneous disease,
more common in adults than in children, may be associated with flushing
and tachycardia, hypotension, syncope, apnea, headache, vomiting,
diarrhea, and/or abdominal pain.5 Mutations in
the c-kit gene have been demonstrated in adult
patients with mastocytosis, but affected children do not tend to have
this mutation.6 The diagnosis of mastocytosis can usually
be confirmed clinically by inducing an urticarial wheal-and-flare reaction
by stroking a lesion (Darier sign); however, this sign is not entirely
specific to mastocytosis. Geimsa or Toluidine blue-stained skin
biopsies demonstrate increased numbers of mast cells.7 The
combination of H1 and H2 antihistamines is used to decrease the
frequency and severity of episodes of mast cell degranulation. Patients
with severe gastrointestinal symptoms may be helped by oral disodium
cromoglycate. Most children with urticaria pigmentosa follow a benign
self-limited course with improvement or resolution occurring during
the first decade. Exposures to medications or physical factors that
induce mast cell degranulation, including aspirin, alcohol, morphine,
codeine, thiamine, scopolamine, polymyxin B, and very hot or cold ...