Journal of the Louisiana State Medical Society
Subcutaneous Fat Necrosis of the Newborn Associated With Hypercalcemia After Therapeutic Hypothermia
Zhuang Feng, MD, PhD; Baofeng Guo, MD; Zhenzhen Zhang, MD, MPH
Subcutaneous fat necrosis of the newborn (SCFN) is a rare, benign, and self-limiting panniculitis of neo- nates that presents in the first few weeks of life and is most commonly associated with birth asphyxia and meconium aspiration. There have been few case reports of SCFN following therapeutic hypothermia. With the increasing use of therapeutic whole-body hypothermia, SCFN may become more prevalent. The dif- ferential diagnosis of SCFN can be broad, and clinicopathologic correlation is essential to make the correct and timely diagnosis. Clinicians should be aware of this rare disease and its potential serious complication hypercalcemia.
CLINICAL FEATURES Subcutaneous fat necrosis of the newborn (SCFN) is a rare, benign, and self-limiting panniculitis of neonates that presents in the first few weeks of life. It mainly affects term and post-term neonates. Neonatal risk factors include hy- poxia, meconium aspiration, sepsis, hypothermia, obstetric trauma, anemia, and thrombocytopenia; maternal risk factors include gestational diabetes, preeclampsia, smoking, and family history of thrombosis. 1,2 Cold exposure is a known risk factor for SCFN. As therapeutic hypothermia has been becom- ing a routine protocol for hypoxic ischemic encephalopathy (HIE) in neonatal intensive care units, SCFN as a complica- tion of whole-body cooling has been increasingly reported in the past several years. 3-8 Studies reporting its incidence are limited. In a study by Strohm et al., 12 (1%) of 1,239 newborns with therapeutic whole-body hypothermia developed SCFN. 8 Shankaran et al. reported 1 (1%) of 102 newborns with thera- peutic whole-body hypothermia developed SCFN. 9 SCFN usually presents as circumscribed, erythematous, indurated nodules and plaques on fat-bearing areas such as face, chest, back, buttocks, arms, and thighs; fluctuant skin lesion was rarely reported. 6 The skin lesions are often pain- less and not warm to palpation. Pain was seen in 25% of patients in one case series. 1 The skin lesions usually appear 2-10 days after the completion of cooling therapy. 3,4,6,7,10,11 The skin lesions usually resolve spontaneously in weeks to months, but hematoma formation requiring skin debridement and grafting was rarely reported. 8 Complications of SCFN include dyslipidemia, hypoglycemia, thrombocytopenia, and hypercalcemia. 1,5 The most serious complication, hy- percalcemia, may occur several days to six months after the
onset of skin lesions. 1,6,12 Hypercalcemia as a complication of SCFN has been seen in 20%-69% of patients in previous case series. 1,2,12 Strohm et al. reported hypercalcemia was seen in 8 (67%) of 12 SCFN patients after therapeutic hypothermia. 8 Clinically, hypercalcemia manifests from asymptomatic to irritability, weight loss, hypotonia, lethargy, poor feeding, dehydration, and growth retardation. 3,11,13 In severe cases, metastatic calcification occurs in kidney, myocardium, major vessel, liver, and brain. 1,8,12 PATHOLOGIC FINDINGS The diagnosis of SCFN is based on clinicopathologic correlation and histopathologic examination of skin punch biopsy. SCFN characteristically shows a lobular panniculitis with a dense infiltrate of lymphocytes, histiocytes, multi- nucleated giants cells and occasional eosinophils, and radially arranged needle-shaped clefts in adipocytes and histiocytes. 14 The needle-shaped clefts represent triglyceride crystals that are extracted during specimen processing; the crystals are derived from stearic and palmitic acids, normal components of neonatal subcutaneous adipose tissue. In late stage of the disease, septal fibrosis and calcification can be seen in the fat lobules. Fine-needle aspiration and touch imprint cytology of drainage material have been used as alternative tools for diagnosis in few case reports. 15 Aspiration and drainage can provide quick and less invasive evaluation, but the sensitiv- ity is limited compared to skin biopsy. Cytology findings consist of fat droplets containing radially arranged refractile needle-shaped crystals in a background of inflammatory cells, including lymphocytes, histiocytes, andmultinucleated
J La State Med Soc VOL 166 May/June 2014 97
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