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Characteristic findings on physical examination
Subcutaneous fat necrosis of the newborn (SCFN) is a panniculitis that presents with firm indurated nodules or plaques especially in areas with large amounts of fat such as cheeks, thighs, buttocks, upper arms and trunk (Figure 1). The stress of birth is usually the cause of SCFN so the fat necrosis is not typically present at birth but instead appears a few days and rarely up to weeks after birth. The onset after birth helps differentiate SCFN from many congenital tumors.
The overlying skin in SCFN is inflamed and red and the nodules may suppurate. The child is otherwise well with no fever. The differential diagnosis includes other causes of panniculitis, tumor or abscess but the clinical picture of a healthy, afebrile child with a history of either fetal anoxia, hypothermia, or difficult labor is supportive.
Expected results of diagnostic studies
Skin biopsy or fine needle aspirate is pathognomonic showing fat necrosis with needle-shaped clefts within the fat cells (Figure 2, Figure 3). A biopsy must be deep enough to include the subcutaneous tissue; a shave biopsy is inappropriate. Fine needle aspiration or core biopsy is also a reasonable and less invasive technique if fat can be obtained and interpreted. The diagnosis can often be made clinically.
The differential diagnosis includes the following:
Abscess: The infant is often febrile or ill, the area may feel more fluctuant, ultrasound can help determine if there is fluctuance. When in doubt biopsy with culture and empiric antibiotics are reasonable.
Congenital tumors such as myofibroma, fibrosarcoma, congenital hemangioma, lipoma or other vascular tumors are typically present congenitally and will not improve as SCFN does. An ultrasound, biopsy or aspiration can help when in doubt.
Panniculitis: Most other causes of panniculitis are not seen in the neonatal period. If deemed necessary, skin biopsies should help classify the type of panniculitis.
Sclerema neonatorum is a more diffuse hardening of the subcutaneous tissue in critically ill and typically preterm neonates and is extremely rare with modern medicine.
Who is at Risk for Developing this Disease?
Nearly any cause of birth trauma, hypoxemia, fetal stress or cold exposure (such as fetal cooling in the setting of neural depression) may lead to SCFN.
The most typical history is of a large baby who had a difficult delivery due to fetal pelvic disproportion with prolonged labor, fetal hypoxemia or other birth trauma. Areas especially rich in brown fat which are then crushed during birth such as those over boney prominences seem to be most at risk.
Other associations include preeclampsia, gestational diabetes, meconium aspiration, maternal use of cocaine or calcium channel blockers and prolapsed umbilical cord. Administration of PGE1 for cyanotic heart disease has been associated with fat necrosis.
SCFN can happen after caesarean section if there are other stresses or if labor was attempted and failed.
What is the Cause of the Disease?
SCFN is likely due to trauma or hypoxemia to saturated fats that are abundant in newborns. Newborns have a higher percentage of saturated fats that have a higher melting point. Therefore, the fat will crystalize at higher temperatures than in adults and only slight cooling can cause SCFN.
Systemic Implications and Complications
Large areas of SCFN may suppurate and take weeks to heal but typically smaller lesions will heal rapidly (within days or weeks). As the lesions heal, there can be a release of large amounts of calcium possibly due to macrophage activation. This calcium is often not clinically relevant but can rarely lead to kidney stones, renal disease, hypercalcemic seizures or death. Occasionally poor growth can result. The cause of hypercalcemia is not entirely clear but may be excess secretion of 1,25-dihydroxyvitamin D caused by the granulomatous inflammation.
The skin lesions do not typically require therapy. The disease will self-resolve often with no scarring. Rarely with suppuration, wound care and monitoring for infection is needed. Symptomatic or rapidly worsening hypercalcemia can be treated with furosemide, bisphosphonates or systemic steroids. Therapy is rarely necessary.
Optimal Therapeutic Approach for this Disease
Most SCFN will self-resolve and requires no therapy.
All infants should have calcium monitoring and the levels should be followed frequently until they trend down. Typically, monitoring weekly until a down trend is noted is sufficient with spaced out checks until normal. Ionized calcium may be more accurate as it does not depend on fetal albumin levels. If there is a trend up which approaches critical levels a pediatric endocrinologist or intensivist should help guide therapy with fluids, diuretics, and systemic steroids, and occasionally bisphosphonates may be needed. Bisphosphonate dosage is variable depending on the severity and age of the child and should be guided by a pediatric endocrinologist or intensivist. Renal function, triglycerides, platelet count and other electrolytes may need to be followed as well.
The skin lesions are often self-limited but if they suppurate, local wound care with petrolatum gauze and monitoring for infection is typically all that is needed. Extensive debridement should be avoided. Rarely grafting has been done for larger lesions.
Most important in monitoring is to evaluate for hypercalcemia. The hypercalcemia may occur weeks to months after the SCFN starts and even resolves. The trend of calcium levels should be followed weekly for a few weeks and then monthly for 3-4 months depending on the trend. If there is a rapid rise, testing should be done more often and if the calcium levels never rise or trend down, the tests can be done less often.
Unusual Clinical Scenarios to Consider in Patient Management
SCFN can occur over the spine due to compression of fat by the bony processes of the spine. Midline nodules in neonates should be biopsied only with extreme caution especially in the lumbosacral area, in case the lesions are not SCFN and have a connection to the underlying CNS.
Presentation with widespread suppurating skin lesions can be ominous-looking but these patients still typically do well with supportive care including monitoring for infection and calcium levels.
What is the Evidence?
Oza, V, Treat, J, Cook, N, Tetzlaff, MT, Yan, A. “Subcutaneous fat necrosis as a complication of whole-body cooling for birth asphyxia”. Arch Dermatol. vol. 146. 2010. pp. 882-5. (Whole body cooling is being used much more widely for neural depression, and therefore, SCFN may become much more common.)
Burden, AD, Krafchik, BR. “Subcutaneous fat necrosis of the newborn: a review of 11 cases”. Pediatr Dermatol. vol. 16. 1999. pp. 384-387. (This is a great large review of the salient features of a series of patients with SCFN.)
Mahé, E, Girszyn, N, Hadj-Rabia, S, Bodemer, C, Hamel-Teillac, D, De Prost, Y. “Subcutaneous fat necrosis of the newborn: a systemic evaluation of the risk factors, clinical manifestations, complications and outcome of 16 children”. Br J Dermatol. vol. 156. 2007. pp. 709-715. (This is an excellent larger review of the salient features of a series of patients with SCFN.)
Finne, PH, Sanderud, J, Aksnes, L, Bartlid, D, Aarskog, D. “Hypercalcemia with increased and unregulated 1,25-dihydroxyvitamin-D production in a neonate with subcutaneous fat necrosis”. J Pediatr. vol. 112. 1988. pp. 792-794. (The hypercalcemia in SCFN remains not fully explained; this article looked at 1,25-dihydroxyvitamin-D production as a source.)
Carraccio, C, Papadimitriou, J, Feinberg, P. “Subcutaneous fat necrosis of the newborn: link to maternal use of cocaine during pregnancy”. Clin Pediatr. vol. 33. 1994. pp. 317-318. (Since most of these infants are big for age, resulting in difficult labor, it is good to be able to explain SCFN in the typically small premature babies exposed to cocaine.)
Alos, N, Eugene, D, Fillion, M, Powell, J, Kokta, V, Chabot, G. “Pamidronate: Treatment for severe hypercalcemia in neonatal subcutaneous fat necrosis”. Horm Res.. vol. 65. 2006. pp. 289-94. (This article details the use of a bisphosphonate for very severe SCFN.)
Rice, AM, RIvkees, SA. “Etidronate therapy for hypercalcemia in subcutaneous fat necrosis of the newborn”. J Pediatr. vol. 180. 1999. pp. 250-254. (This article also details the use of a bisphosphonate for very severe cases of SCFN.)
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