Subcutaneous fat necrosis of the newborn (SFNN) is an uncommon disorder characterized by firm, mobile, erythematous nodules and plaques over the trunk, arms, buttocks, thighs, and cheeks of full-term newborns. [1, 2] The nodules and plaques appear in the first several weeks of life. Subcutaneous fat necrosis of the newborn usually runs a self-limited course, but it may be complicated by hypercalcemia and other metabolic abnormalities. [1, 2]
The exact pathogenesis of subcutaneous fat necrosis of the newborn (SFNN) is not known. It is postulated that cold or stress-induced injury to immature fat cells results in the development of solidification and necrosis. A granulomatous infiltrate forms, which, through various pathways, may lead to life-threatening hypercalcemia. Staining of biopsy specimens demonstrates increased levels of 1alpha-hydroxylase within the granulomatous infiltrate, as is seen in other granulomatous conditions such as sarcoidosis.  Alpha-hydroxylase promotes the conversion of 25 OH D3 to its active form 1,25 OH 2D3; the latter increases intestinal absorption of calcium and calcium mobilization from bones, potentially leading to hypercalcemia. [1, 4, 5] Elevated levels of prostaglandin (PG) E2 have been reported in subcutaneous fat necrosis of the newborn.  and may contribute to hypercalcemia through a different pathway.
Alternative explanations for hypercalcemia include the release of calcium from necrotic fat cells or elevated parathyroid hormone (PTH) levels that indirectly increase serum calcium by promoting osteoclast activity.  A child with cyanotic heart disease treated with prostaglandins (intravenous PGE1) to maintain patent ductus arteriosus developed subcutaneous fat necrosis of the newborn; when the PGE1 was discontinued, the subcutaneous fat necrosis of the newborn resolved.  Elevated prostaglandins contribute to the inflammatory cascade that follows, marked by thrombocytopenia, high acute-phase reactants such as C-reactive protein, and fever. [8, 9] The latter has been attributed to increased levels of PGE2 and granuloma production of interleukin 1.
Frequency is unknown; subcutaneous fat necrosis of the newborn (SFNN) is rare.
Race does not play a role.
Sex does not play a role.
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