By Jusleen Ahluwalia, MD, and Lawrence F. Eichenfield, MD
Subcutaneous fat necrosis of the newborn
The clinical history and morphology of our patient’s cutaneous manifestation is highly suggestive of subcutaneous fat necrosis of the newborn (SFN). SFN is a self-limited, lobular form of panniculitis that typically affects newborns at term or post term until the first 6 weeks of life.1 Delivery complications resulting in perinatal stress – including perinatal hypothermia, hypoxia, and birth trauma – have been associated with the development of SFN.2 Other risk factors include maternal disorders during pregnancy, such as diabetes, hypertension, exposure to tobacco, and thrombotic events. 1,2 SFN has been noted after therapeutic hypothermia that is utilized to minimize neurologic effects of neonatal hypoxic ischemic encephalopathy. 1
It has been hypothesized that SFN follows hypoxic injury to fat caused by local trauma, while in some cases it is proposed that SFN results from an imbalance of saturated and monounsaturated fats leading to crystallization at certain temperatures in the neonatal subcutis. 1
The clinical presentation of SFN is characterized by the development of one to several erythematous violaceous subcutaneous nodules and plaques that can evolve into firm calcifications, and may be tender to palpation. They are characteristically located on the shoulders, back, and upper limbs. Spontaneous regression has been observed without scarring within 2-5 months; however, cutaneous atrophy of the affected areas can follow recovery from the condition. 1-3
Hypercalcemia is a potentially fatal complication of SFN that infrequently occurs in a subset of patients. Its risk increases with the extent of perinatal injury and degree of fat necrosis. 1 Several studies have documented a prevalence of hypercalcemia in 36%-56% of infants with SFN; however, most of these cases were mild and conservatively managed. 2,4 Hypercalcemia may manifest without symptoms or present with vomiting, irritability, and seizures. 1 Nephrocalcinosis can complicate high calcium levels and is detected by abdominal ultrasonography. Other complications that can accompany the development of SFN include thrombocytopenia, hyperglycemia, and hypertriglyceridemia, although this relationship is controversial as these conditions can be attributed to other neonatal disease or maternal factors. 5
Differential diagnosis
Although SFN is generally a transient, self-limited condition, recognition of SFN is critical to monitor and avoid metabolic alterations associated with SFN. Sclerema neonatorum is another rare condition characterized by diffuse hardening of the skin affecting infants up to 4 months of age with severe underlying disease and systemic symptoms. 1
Deep soft tissue infections, such as cellulitis, are usually accompanied with fever and other signs of infection.1 Mechanical trauma may induce firm, subcutaneous nodules in areas where fat is adjacent to bone and should be considered in any infant or child with subcutaneous nodules over areas prone to injury. 1 Sudden withdrawal of systemic steroids can cause subcutaneous nodules typically located on cheeks, arms, and trunk. 1
Management
Most infants with SFN are managed conservatively. 1 Recently proposed guidelines for the management of SFN include weekly monitoring of calcium levels until 1 month of age and monthly until 6 months of age or after resolution of the cutaneous lesion, and more frequently if hypercalcemia is documented. Platelet count and creatinine, glucose, and triglyceride levels also should be assessed. 5 At-risk infants should be evaluated for nephrocalcinosis with abdominal ultrasonagraphy. 1,6 Treatment of hypercalcemia can consist of modification of diet with low levels of calcium and vitamin D, intravenous saline, calcium-wasting diuretics, or occasionally corticosteroids. Bisphosphonates also have been reported to successfully treat hypercalcemia in the setting of SFN. 1,6