with a low specific gravity They may become severely dehydrated if the weight loss is in excess of 3% to 5% Constant observation should be maintained during the water deprivation test to ensure patients not covertly consume water and to prevent severe dehydration A trial of intranasal desmopressin (DDAVP) should distinguish between DI and nephrogenic DI because patients with antidiuretic hormone–deficient DI will respond to the exogenous hormone Unfortunately, even these tests are fraught with inaccuracies Patients with primary polydipsia who have chronic overhydration and diminished capacity to concentrate urine may have a blunted response to water deprivation In addition, patients with DI and nephrogenic DI may produce hypertonic urine if the glomerular filtration rate is decreased as severe dehydration ensues Radioimmunoassay for antidiuretic hormone can be helpful in confusing cases TABLE 64.3 LIFE-THREATENING CAUSES OF POLYDIPSIA Diabetes insipidus (antidiuretic hormone deficient) Nephrogenic diabetes insipidus Diabetes mellitus Primary polydipsia Suggested Readings and Key References Cermeroglu AP, Buyukgebiz A Psychogenic diabetes insipidus in toddlers with compulsive bottle-drinking: not a rare entity J Pediatr Endocrinol Metab 2002;15(1):93–94 Dabrowski E, Kadakia R, Zimmerman D Diabetes insipidus in infants and children Best Pract Res Clin Endocrinol Metab 2016;30(2):317–328 Di Iorgi N, Allegri A, Napoli F, et al Central diabetes insipidus in children and young adults: etiological diagnosis and long-term outcome of idiopathic cases J Clin Ednocrinol Metab 2014;99(4):1264–1272 Dundas B, Harris M, Narasimhan M Psychogenic polydipsia review: etiology, differential, and treatment Curr Psychiatry Rep 2007;9(3):236–241 Kavanagh C, Uy N Nephrogenic diabetes insipidus Pediatr Cl N Am 2019;66(1):227–234 Rose S, Auble B Endocrine changes after pediatric traumatic brain injury Pituitary 2012;15(3):267–275 CHAPTER 65 ■ RASH: ATOPIC/CONTACT DERMATITIS AND PHOTOSENSITIVITY JOY WAN DERMATITIS Dermatitis is the general term used to describe an itchy, eczematous rash In its acute form dermatitis is characterized by erythema, edema, exudation, scattered papules or vesicles, scaling, and crusting Chronic dermatitis is characterized by lichenification (accentuated skin markings), hyperpigmentation, hypopigmentation, and excoriations Diagnosis of the underlying cause of the dermatitis relies on patient history and physical examination findings; histology is typically nonspecific This chapter highlights common causes of dermatitis in children, including atopic dermatitis, nummular eczema, asteatotic eczema, dyshidrotic eczema, lichen simplex chronicus, and contact dermatitis Atopic Dermatitis Atopic dermatitis is the most common cause of dermatitis in children ( Table 65.1 ), occurring in 10% to 20% of children It is a chronic and relapsing condition characterized by pruritic eczematous papules, patches, and plaques There is often a personal or family history of allergic rhinitis, hay fever, or asthma Many patients have the onset of symptoms before months of age, with most developing symptoms by years of age Heat, stress, sweating, infection, and exposure to environmental (e.g., pet dander, pollen) and contact allergens (e.g., fragrances, soaps) may precipitate flares The diagnosis is mainly based on typical history and physical examination findings, and the American Academy of Dermatology has developed criteria to summarize these features ( Table 65.2 ) The broad differential diagnosis requires the exclusion of other skin conditions that present in a similar fashion, including seborrheic dermatitis, scabies, psoriasis, nutritional deficiencies (i.e., zinc), immune deficiencies, and cutaneous lymphoma Importantly, while superficial bacterial infections, seborrheic dermatitis, and contact dermatitis may occur in isolation, they may also coexist in a patient with atopic dermatitis The typical distribution can vary by age Infants have lesions on the cheeks, trunk, and extensor surfaces Children show involvement of the hands, feet, and flexor areas, such as the antecubital and popliteal fossae, and the neck ( Fig 65.1 ) In adolescents and adults, flexor areas, hands, and feet are often involved Xerosis (dry skin), ichthyosis vulgaris (inherited fish-like scaling of the extremities and hyperlinear palms), keratosis pilaris (follicularly based papules with cornified plugs in the upper hair follicles), infraorbital eyelid folds (Dennie–Morgan sign), pityriasis alba (scaly hypopigmented macules and patches on the cheeks), and follicular accentuation may be seen The main factors to assess when caring for patients with atopic dermatitis include pruritus, superinfection, and concomitant contact dermatitis The pruritus of atopic dermatitis may be severe, resulting in sleep disturbances in the child and caretakers and difficulty concentrating in school and work The persistent itch-scratch cycle can also lead to severe excoriations in the skin This damage to the skin barrier, along with inherent defects in the skin barrier and immunity that are associated with atopic dermatitis, makes patients particularly susceptible to superinfections with bacteria (Staphylococcus aureus or group A streptococcus), yeast (candida), and viral infections (herpes simplex, enterovirus, and molluscum contagiosum) The defective skin barrier in atopic dermatitis allows increased penetration of contact allergens that is felt to explain the increased incidence of contact dermatitis in this population (see below) Management of atopic dermatitis includes minimizing triggers (irritants and allergens) with “gentle skin care,” including an unscented soap, fragrance-free laundry detergent, hypoallergenic shampoo and conditioner, and regular application of thick unscented emollients immediately after bathing Repeated screening for new trigger contactants is important because care providers may try new topical products in an effort to provide relief Screening for infection is critical in all patients with atopic dermatitis flares, including culturing active pustules for bacteria and obtaining a viral culture or polymerase chain reaction (PCR) sample from vesicles or erosions for herpes simplex virus, and in some cases, enterovirus For localized areas, use of a topical antibiotic that covers gram-positive organisms is important Empiric oral antibiotic or antiviral treatments may be needed in more involved cases Dilute bleach baths are helpful in decreasing skin bacterial colonization and infections in atopic dermatitis and may help minimize flares Atopic dermatitis on the cheeks of infants is best managed by applying petrolatum-based ointments as a barrier prior to feeding and sleeping, avoidance of irritants (e.g., wet wipes, drool, food, pacifiers), and low- to mid-potency topical corticosteroids as needed Topical corticosteroids are the mainstay of treatment for most patients with atopic dermatitis One approach to minimize recurrences of localized atopic dermatitis after flares is to use topical corticosteroids twice daily during flares and then twice weekly for prevention Alternatively, for more diffuse atopic dermatitis, a more practical maintenance therapy may include twice daily use of a low-potency topical steroid compounded into a thick emollient (e.g., hydrocortisone 2.5% ointment mixed 1:1 with petrolatum) Referral to dermatology and/or allergy may be helpful to further manage moderate or severe atopic dermatitis Particularly severe or persistent dermatitis should prompt consideration of an underlying systemic disorder associated with eczematous eruptions, such as immunodeficiencies or nutritional deficiencies