Download Answer to Dermatological Quiz

VOL.11 NO.5
MAY
2006 2007
VOL.12
NO.4
APRIL
Answer to Clinical Quiz
Answer :
1. The diagnosis is urticaria pigmentosa (UP). It is the most common skin manifestation of mastocytosis in both children and adults.
The lesions appear as small, yellow-tan to reddish-brown macules or slightly raised papules or plaques scattered over the body.
Mild trauma, including scratching or rubbing of the lesions, usually causes urtication and erythema around the macules; this is
known as the Darier's sign. This is the reason why the mother noticed urtication and blistering in some of the severe lesions (shown
in the right infra-scapular area at the back) when rubbing dry the baby's body after bath. Patient with mastocytosis may develop
gastrointestinal disease presenting with diarrhoea, abdominal pain and malabsorption. Internal organomegaly affecting the liver
and spleen is rarely seen. Bone and marrow involvement presenting with bone pain, anaemia, leucopenia, thrombocytopenia and
esoinophilia may occur in systemic disease. Fortunately, our baby did not show any symptoms suggestive of systemic involvement.
2. The diagnosis of UP is suspected on clinical grounds and confirmed by histology. Mast cells, which can be shown by special
metachormatic stains such as toluidine blue and Giemsa, are found in increased numbers in dermal papillae, particularly near blood
vessels. The greatest increase occurs beneath UP macules and papules where, on average, there is a fifteen- to twenty fold increase
in mast cells. Hence, rubbing of these lesional macules degranulates the underlying mast cells and produces urtication and blister
when the Darier's sign is elicited. Relevant systemic work up, depending on the signs and symptoms of systemic involvement, may
include complete blood picture, liver and renal function tests, chest x-ray, bone scan/ skeletal survey, GI radio-imaging and
endoscopic studies and bone marrow aspiration.
3. The aim of the treatment is to control mast cell mediator-induced signs and symptoms such as pruritus. H1 receptor antagonists
such as hydroxyzine and doxepin are useful in reducing pruritus, flushing and tachycardia. The addition of H2 antagonists such as
ranitidine or cimetidine may be beneficial. Disodium cromoglycate inhibits degranulation of mast cells and may have some efficacy
in the treatment of mastocytosis. Topical corticosteroids, such a betamethasone diproprionate ointment applied under plastic-film
occlusion may be used to treat extensive UP. Other appropriate treatment is used as indicated to control any systemic disease. As a
group, patients with indolent mastocytosis and skin involvement alone have the best prognosis. Among children with isolated UP,
as in our patient, at least 50 percent of cases resolve spontaneously by adulthood.
Dr. Ka-ho Lau
MBBS(HK), FRCP(Glasg), FHKCP, FHKAM(Med)
Yaumatei Dermatology Clinic, Social Hygiene Service
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