Urticaria pigmentosa

Published on 05/05/2015 by admin

Filed under Internal Medicine

Last modified 22/04/2025

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199 Urticaria pigmentosa

Instruction

Look at this patient’s skin.

Salient features

History

• Urticaria with pruritus on trauma, rubbing or heat: Darier’s sign

• Headache

• Diarrhoea

• Itching.

Examination

• Itchy reddish-brown macules and papules (Fig. 199.1)

• Telangiectasia.

image

Fig. 199.1 Urticaria pigmentosa: reddish-brown macules and papules.

Proceed as follows:

• Look for hepatosplenomegaly.

Diagnosis

This patient has itchy reddish-brown macules with telangiectasia and Darier’s sign (lesions) indicating urticaria pigmentosa (aetiology).

Advanced-level questions

What do you know about urticaria pigmentosa?

It is the cutaneous manifestation of systemic mastocytosis.

What is the histology of urticaria pigmentosa?

It varies from an increase in the number of spindle-shaped and stellate mast cells about the superficial dermal vessels to large numbers of tightly packed round-to-oval mast cells in the upper and mid dermis. Variable fibrosis, oedema and a small number of eosinophils may also be present.

What do you know about systemic mastocytosis?

It is a condition characterized by mast cell hyperplasia that, in most cases, is neither clonal nor neoplastic. It can occur at any age and is slightly more common in men. Four forms have been recognized:

• Indolent form: does not alter life expectancy and constitutes the majority of cases

• Associated with frank leukaemia or dysmyelopoiesis: the prognosis is determined by the underlying haematological disorder

• Aggressive form: the prognosis is determined by the extent of organ involvement

• Mast cell leukaemia: rare, invariably fatal.

What diagnostic tests would you order?

• Urinary histamine is elevated in most cases (an elevated urinary histamine level is not a required finding for a diagnosis of mastocytosis; there is poor correlation between the urinary histamine content and the severity of symptoms in mastocytosis).

• Serum tryptase is elevated in most cases (the tryptase level is elevated in >83% of patients and is highly specific for this disease).

• Coagulation defects may occur as a result of the release of mast-cell heparin.

• Bone marrow biopsy is often diagnostic (revealing the focal infiltration of mast cells).

• Immunohistochemical analysis with monoclonal antibodies against the mast-cell markers tryptase and CD117 is used to confirm the diagnosis.

How would you manage such patients?

Treatment is based on blocking mast cell products, including histamine, prostaglandin D2 and leukotrienes:

• H1 blocker: for flushing and itch (e.g. chlormethiazole)

• H2 blocker: for gastric and duodenal manifestations (e.g. ranitidine, cimetidine)

• Oral sodium cromoglycate for diarrhoea and abdominal pain

• NSAID for flushing not responsive to antihistamines

• High-dose aspirin

• Interferon-alfa has been used for patients with aggressive disease

• Imatinib, an inhibitor of c-Kit tyrosine kinase, also shows promise

• Intravenous cladribine.

FJ Darier (1856–1938), a French dermatologist.

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