diaper rash

• A 15-month-old girl is seen for persistent diaper rash. Despite treatment with zinc oxide cream and topical antifungal cream for over a month, there has been no improvement. The mom also reports that she wants to drink all day long and has doubled the number of wet diapers per day. In the office, she is afebrile with stable vital signs. She is at the 50th percentile for weight and height. On physical examination, there are crusted erythematous and brown papules covering the groin and involving the intertriginous areas. A similar rash is seen on areas of the posterior scalp and axillae. The affected area of the scalp is scaly and seborrheic. The remainder of his physical examination is normal. Initial laboratory test results are as follows:
  • Serum sodium, 146 mEq/L (146 mmol/L); normal range, 136 to 145 mEq/L (136-145 mmol/L)
  • Serum osmolality, 301 mOsm/kg water (301 mmol/kg
  • water); normal range, 275 to 295 mOsm/kg water (275-295 mmol/kg water)
  • Urine specific gravity, 1.001; normal range, 1.001 to 1.035
  • Urine osmolality, 95 mOsm/kg water (95 mmol/kg water); normal range, 300 to 1,000 mOsm/kg water (300-1,000 mmol/kg water

• Of the following, the MOST likely finding in this patient would be
  A. enzyme-linked immunoassay testing positive for human immunodeficiency virus
  B. herpes simplex virus from the culture of the papular fluid
  C. hyphae on potassium hydroxide (KOH) preparation of papular fluid
  D. lytic lesion on radiograph of the skull
  E. serum glucose greater than 300 mg/dL (16.7 mmol

The child described in the vignette with a persistent scalp and diaper rash (Item C171) and symptoms of diabetes insipidus may have Langerhans cell histiocytosis (LCH); therefore, the most likely additional finding would be lytic lesions seen on a skull radiograph.
Histiocytes are cells of the mononuclear phagocyte system. The histiocytoses are rare conditions caused by the abnormal proliferation or functioning of these cells. The most common of these is LCH. The diagnosis of LCH is based on histologic and immunohistochemical criteria and clinical features. The histopathologic features are granuloma containing inflammatory cells and abnormal Langerhans cells. Results of immunohistochemical analysis are positive for CD1a and CD207 (correlates with Birbeck granules). In LCH, cells accumulate and release inflammatory chemokines, which can lead to stimulation of other inflammatory cells and eventually create a “cytokine storm:’ These cytokines contribute to the clinical symptoms. Langerhans cell histiocytosis can occur as a single system or multisystem disease. Single system disease can affect bone (in one or multiple sites) or skin. Multisystem disease is categorized into low-risk and high-risk.
Although LCH can present at any age, the systemic life-threatening form usually occurs in children younger than 4 years. Adults with LCH often have only skin involvement. Skin involvement occurs in 50% of patients and most often appears seborrheic. It can also manifest as papules, vesicles, nodules, and purpuric nodules. Infants with skin-only LCH may progress to multisystem disease, which can be fatal. Any child with seborrheic dermatitis or diaper dermatitis that is persistent should be evaluated for LCH. In children, bone is the most commonly affected organ. The characteristic finding is a lytic lesion in the skull or vertebral collapse. Those with a single bone lesion have an excellent prognosis. Central nervous system and endocrine involvement can also occur. Diabetes insipidus occurs in 24% of patients with LCH due to hypothalamic-pituitary axis disease. Additional findings suggestive of LCH include chronic draining otitis media or chronic mastoiditis.
Multisystem LCH is divided into high-risk and low-risk based on the risk of mortality from disease. High-risk LCH includes patients with disease in 2 or more organs, including at least one of the at-risk organs liver, spleen, lung, and blood (ie, cytopenia). Low-risk LCH is defined as multisystem disease from 2 or more organs but not involving any of the at-risk organs.
Treatment for LCH involves surgical excision, steroid injection, chemotherapy, and radiation, depending on the site of the lesion and how widespread it is.