A TODDLER WITH BROWN PATCHES WHICH URTICATE
A 16-month-old boy presents to the dermatology clinic. His mother has noticed a gradual
accumulation of ‘brown spots’ on his skin. These lesions were not present at birth and the
majority appeared as a crop over a 4-month period around his first birthday. She feels it
is possible that he will continue to acquire new lesions. He had one on his right forearm
which has resolved. She has noticed that some of the lesions appear to ‘blister’ or become
raised after a bath. He is otherwise well; he is thriving and enjoys a full diet. He has no
gastrointestinal symptoms or wheeze. There is no family history of similar skin lesions.
The rest of the family is entirely well.
His height and weight are on the 75th and 91st centiles for his age, respectively. He is cooperative
and follows directions. He has diffuse, scattered, monomorphic, small oval-round
reddish-brown macules concentrated predominantly over his anterior and posterior trunk,
but also extending to his neck and with a few scattered lesions on his limbs. There are more
than 40 of these lesions. One lesion just below his xiphisternum, when rubbed, became transiently
erythematous and swollen (urticaria), a positive Darier’s sign (Fig. 10.1). Examination
of his cardiorespiratory system and abdomen is normal. He has no lymphadenopathy.
These lesions represent multiple mastocytomas and the eruption is referred to as urticaria
pigmentosa. Darier’s sign describes the development of a wheal and surrounding
erythema in a lesion after rubbing (physical degranulation of histamine from mast cells).
Mastocytosis is the abnormal accumulation of mast cells within the skin and rarely other
organs (liver, spleen or lymph nodes). The differential diagnosis would include lentigines
or melanocytic naevi (if Darier’s sign negative) or xanthogranuloma, histiocytosis X or
generalized eruptive histiocytoma (if the lesions were raised or indurated).
All forms of mastocytosis in children have a good prognosis and systemic involvement is
rare. The majority of cases resolve spontaneously. In adults, however, systemic involvement
may be aggressive or even represent a mast cell leukaemia. Symptoms of systemic
involvement or of acute degranulation of widespread cutaneous disease include flushing,
diarrhoea, nausea/vomiting, abdominal cramps and wheeze. Adults may also complain of
syncope, angina, headaches and bone pain.
Although this young patient has no symptoms of systemic disease, basic investigations
would be justified including particularly full blood count, serum tryptase and liver function
tests. A skin biopsy can be performed if there is diagnostic doubt. Mast cell infiltrates
can be difficult to identify by routine haematoxylin & eosin staining, and special stains
such as Giemsa or toluidine blue, which demonstrate metaochromatic staining of mast
cells, are required. For patients with rapidly progressive disease and abnormalities of the
above investigations, further testing such as bone marrow aspirate and biopsy under the
supervision of the haematology department may be indicated. Demonstration of activating
mutations of the c-kit proto-oncogene would help tailor therapy in aggressive or
leukaemic disease (e.g. imatinib).
As the skin lesions are likely to resolve spontaneously by the boy’s 10th birthday, no
treatment is indicated. For patients with skin symptoms antihistamines (H1-blocker) may
be helpful. Moderate sunlight exposure can hasten the resolution of diffuse lesions and
psoralen–UVA can be offered to adults/older children. Patients with numerous lesions or
diffuse disease should avoid mast cell degranulating agents such as non-steroidal antiinflammatory
drugs, opiates, alcohol, caffeine, radiological contrast media and abrupt
physical degranulation such as a hot bath or other acute temperature change, vigorous
rubbing (e.g. after a bath or by tight clothing). Exposure to degranulating agents or to
allergens (such as hymenoptera stings) can potentially provoke anaphylaxis.