Mast cells are normally distributed in the connective tissue of the skin and other organs. These cells release many substances, including histamines, from their granules. An increase in the number of mast cells is referred to as mastocytosis. It may be confined to the skin or, less frequently, may be widespread through all tissues including the viscera (systemic mastocytosis).

Cutaneous mastocytosis

Cutaneous disease is seen principally in children, whereas associated systemic disease is more common in adults. There is a positive correlation between a late onset III adult life, extent of skin involvement and systemic disease.
Clinical forms of the disease that affect principally the skin are varied. Cells may be concentrated into a tumour, often a solitary nodule of yellow/brown colour (mastocytoma). This occurs on the trunk or limbs in the first few years of life and regresses after an interval of 3-  years.
In urticaria pigmentosa, macular or papular pigmented red/brown lesions are widely distributed on the trunk and are more sparse on the limbs. These lesions urticate on scratching. Trauma to the non-lesional skin may produce dermographism in many patients. Attacks of flushing or irritation of the skin may follow emotional upset or change of temperature or be precipitated by alcohol or drugs that release histamine, such as codeine or aspirin. The majority of cases occur in children and the lesions fade in late childhood, but those patients with an onset in adult life tend not to lose their disease. Children may be born with or develop in early infancy diffuse cutaneous mastocytosis, and blistering may be the first indication of the disease. Later in childhood the skin may be thickened and leathery, when markings and folds are exaggerated. Individual lesions are not seen and very rarely erythrodermic forms occur. Hepatomegaly and splenomegaly may occur with diffuse disease. In adults an uncommon variant of urticaria pigmentosa occurs in which the predominant skin change is widespread telangiectasia. Pigmented lesions are small and macular and are associated with erythema. In systemic disease the bone marrow and skeletal system are commonly involved but any organ can be affected, giving rise to symptoms such as headache and bronchospasm due to histamine release. The treatment is symptomaticand the prognosis is good in the majority.


This is an acute and sometimes recurrent panniculitis that produces painful nodules or plaques on the shins (Fig. 20.6), with occasional spread to the thighs or arms. Adult females are principally affected. Some causes are shown in Table 20.3; in nearly 50% no cause is found. Histological features suggest that this is an immunological reaction. Immune complex deposition within dermalvessels is an important component in the production of the symptom complex.


Painful nodules or plaques up to 5 ern in diameter appear in crops over 2 weeks and slowly fade to leave bruising and staining of the skin. Systemic upset is common, with malaise, fever and arthralgia; the condition is especially debilitating when it is recurrent.


Investigations should attempt to exclude streptococcal disease, sarcoidosis and viral causes. The association with sarcoidosis.



Bed rest helps when systemic features and arthralgia are present. NSA1Ds such as indomethacin should be given to lessen the pain associated with the cutaneous and joint symptoms. Recovery may take weeks and recurrent attacks can occur.


This is an acute self-limiting and often recurrent condition affecting the skin and mucosal surfaces. There evidence suggesting that circulating immune complexes are important in triggering the reaction in the skin, which occurs 7-14 days following, for example, recurrent herpes simplex infection.


Children, adolescents or young adults are principally affected. It is associated with:
HERPES SIMPLEX INFECTION (usually type 1) in about one-third of cases. The virus is a common trigger factor for recurrent attacks.
MYCOPLASMA PNEUMONIAE. DR UG s, e.g. sulphonamides, sulphonylurea derivatives (chlorpropamide) and, less commonly now, barbiturates.
OTHER INFECTIONS, including vaccinia or orf, streptococci, yersiniosis, tuberculosis and histoplasmosis.
CONNECTIV -TISSUE DISEASES OR NEOPLASIA (rare precipitating factors).
TOPICAL APPLICATIONS triggering allergic reactions over the areas of skin on which they are placederythema multiforme lesions occur at the peripheries. In half of the cases no cause can be found.

Symmetrically distributed erythematous papules evolve into concentric rings of varying colour. These are commonly seen on the back of the hands, palms and forearms, but may also be seen on the feet or toes. The lesions may show central pallor associated with oedema, bullaeformation and peripheral erythema. Alternatively, pallor  may be accompanied by central erythema or purpura.  rank bullae represent epidermal necrosis and the separation of this layer. Lesions often spread proximally alongthe limbs or affect dependent parts in prostrated patients.Sever e mucosal disease is seen with Mycoplasma pneumoniae  infection for example, and peripheral lesions may be few in number and difficult to discern, so that erythema multi forme may not easily be diagnosed. Eye changes include conjunctivitis, ulceration of the cornea, uveitis or panophthalmitis, so that the opinion of an ophthalmologist should be sought in the early stages of disease. These latter features are often the most serious of the complications associated with erythema multiforme. The Stevens-Johnson syndrome describes a severe erythema
multiforme with a widespread bullous disease associated with oral and genital ulceration and marked constitutional symptoms.


The disease is usually self-limiting but death can occur with the Stevens-Johnson syndrome. The withdrawal of offending drugs and the prompt treatment of associated disease is important. It is unlikely that systemic steroid therapy alters the outcome, and such treatment has been shown to be disadvantageous in children. Care of the eye and mucosal ulceration are important, and in severe cases intravenous fluids and feeding may be required.

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