The most frequent clinical form of mastocytosis was urticaria pigmentosa followed by mastocytoma and diffuse cutaneous mastocytosis. Darier's sign was present in 94% of cases. A negative Darier's sign does not rule out mastocytosis. In contrast to adults, mastocytosis in children usually has a benign course making sophisticated or invasive diagnostic tests unnecessary. A classification of paediatric cutaneous mastocytosis is proposed.

Key Points HVLL is a chronic EBV+ lymphoproliferative disorder of childhood with risk to develop systemic lymphoma. The disease shows favorable response to conservative therapy despite the presence of a T- or NK-cell monoclonal proliferation.

The so‐called KID (keratitis, ichthyosis, deafness) syndrome is a congenital disorder of ectoderm that affects not only the epidermis, but also other ectodermal tissues such as the corneal epithelium and the inner ear. Sixty‐one patients who fulfill the criteria for this syndrome were identified in a review of the literature through December 1993. All had cutaneous and auditory abnormalities, and 95% also had ophthalmologic defects. The most frequent clinical features were neurosensory deafness 90%, erythrokeratoderma 89%, vascularizing keratitis 79%, alopecia 79%, and reticulated hyperkeratosis of the palms and soles 41%. All of these findings constitute the major criteria for the diagnosis. The KID acronym does not accurately define this entity since the disorder is not an ichthyosis, because scaling is not the main cutaneous feature and not all patients have keratitis early in the course. We suggest that this syndrome should be included under the general heading of congenital ectodermal defects as a keratodermatous ectodermal dysplasia (KED).

Of the patients with epidermal nevi, 10-18% may have disorders of the eye, nervous, and musculoskeletal systems. A predisposition to malignant neoplasms in ectodermal and mesodermal structures may also be found. There are six different epidermal nevus syndromes described so far: Proteus, congenital hemidysplasia with ichthyosiform nevus and limb defect syndrome, phakomatosis pigmentokeratotica, sebaceous nevus, Becker nevus, and nevus comedonicus. Thirty-five patients with epidermal nevus syndrome seen at the National Institute of Pediatrics in Mexico City during a 31-year period are described. This syndrome represented 7.9% of 443 patients with epidermal nevi; its relative frequency was 1 case per 11,928 pediatric patients and 1 case per 1080 dermatologic patients. Nine epidermal nevus syndrome patients (26%) had Proteus syndrome. Sebaceous nevus syndrome was found in six patients (17%), while the nevus comedonicus syndrome was found in three (8%). Two patients were diagnosed with phakomatosis pigmentokeratotica and one patient with congenital hemidysplasia with ichthyosiform nevus and limb defect syndrome. This is the first report of phakomatosis pigmentokeratotica and congenital hemidysplasia with ichthyosiform nevus and limb defect syndrome in Mexican patients. One patient had an inflammatory linear verrucous epidermal nevus with systemic involvement. Thirteen patients (37%) had keratinocytic nevi with systemic involvement. We propose the keratinocytic nevus syndrome to be defined as the association of a keratinocytic nevus with neuronal migration and/or musculoskeletal disorders in addition to a higher risk for mesodermal neoplasms.

Dermoid cysts (DCs) are benign cutaneous tumors that tend to persist and grow. The aim of this study was to examine the clinicopathologic features of congenital DCs. We present a case series of 75 children with a clinicopathologic diagnosis of DC. Seventy-two cysts were located on the head, one on the neck, and two on the trunk. Six cysts were located along the midline. Eight patients had symptoms other than changes in cyst size. Imaging studies were performed on 15 patients. Surgical excision was the primary treatment in all 75 cases. Neurosurgery and ophthalmology services were involved in the care of some patients. Histopathologic studies reported a foreign body giant cell reaction in 17 of the cysts. No recurrence was documented. DCs can remain stable for years, but they can become symptomatic as a result of enlargement and rupture or, more rarely, as a result of extension into surrounding tissues. Physicians should be aware that certain locations have a higher risk of DC extension, and adequate diagnostic investigations should be performed before their complete resection.