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A 50-year-old woman presented with itchy, multiple, flat, yellowish, waxy papules and plaques diffusely involving her face, trunk, and upper extremities for 5 years (Fig. 1). Itching was moderate to severe in intensity and was episodic, without any identifiable aggravating or relieving factors. On rubbing the lesions with a blunt object erythema was elicited. Her ophthalmological examination was normal. Her complete hemogram was normal along with other routine investigations. Patient's slit skin smear for acid-fast bacilli and rk39 dip-stick ELISA for post-kala-azar dermal leishmaniasis were negative. Ultrasound examination of her abdomen was normal and skeletal survey showed no evidence of bony changes. Histological examination showed diffuse dense infiltrate of numerous mast cells filling up the papillary dermis and most of upper- and mid-reticular dermis. Overlying epidermis showed moderate epidermal hyperplasia and hyperpigmentation. There was sparse scattering of neutrophils within the infiltrate. Extracellular mast cells granules were also seen (Fig. 2). Diagnosis of diffuse cutaneous mastocytosis of pseudoxanthomatous variety was made.
Figure 2. Histopathology showing dense diffuse infiltrate of numerous mast cells filling up the papillary dermis and most of the upper and mid-reticular dermis (H&E; a, ×100; b, ×400)
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The patient was prescribed treatment in the form of H1 and H2 blockers (fexofenadine and ranitidine) and trimethylpsoralen and ultraviolet A (PUVA) photochemotherapy. After 2 months of treatment, there has been marked improvement in the appearance and itching.
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Cutaneous mastocytosis is a rare disorder. Clinical varieties are urticaria pigmentosa, mastocytoma, diffuse cutaneous mastocytosis, and telangiectasia macularis eruptiva perstans in order of decreasing frequency of occurrence.1 Diffuse cutaneous disease has two clinical variants: bullous and pseudoxanthomatous or xanthelesmoid types.2
Pseudoxanthomatous mastocytosis was first described by Tilbery in 1875.3 It is characterized by multiple, pale, flat, yellowish papules and nodules, varying in size from 1 mm to 2 cm.4 This multinodular nonpigmented variety of mastocytosis is extremely rare. In this variety, as against a classic Darier's sign, only erythema without urtication is elicited by rubbing.5 Skin biopsy reveals dense dermal infiltrate of mast cells. Diagnosis is confirmed on the basis of clinical features and characteristic histopathological findings. Clinical differential diagnosis includes pseudoxanthoma elasticum3 and, in tropical countries, lepromatous leprosy and post-kala-azar dermal leishmaniasis.
Treatment options include antihistamines, avoidance of trigger factors, topical or systemic corticosteroids, mast cell stabilizers, PUVA therapy, and interferons. The prognosis depends on the age of onset and systemic involvement.6 Earlier age of onset and absence of systemic involvement are suggestive of better outcome. Childhood disease may resolve spontaneously. With advancing age, there is risk of extracutaneous involvement and of development of malignancies.5 Although upon treatment, itching and lesions have shown improvement in this case, the disease may persist or even worsen and therefore long-term prognosis remains guarded.