Keywords
subcutaneous fat necrosis of the newborn - light polarization - gout - Lesch–Nyhan syndrome - skin nodules
Image and Case Description
This figure is a composite view from subcutaneous nodules with changes typical of “subcutaneous fat necrosis of the newborn” (SFNN) from a 15-month-old girl. It shows degenerated fat surrounded by mild infiltrates of chronic inflammation and multinucleated foreign body giant cells. Unlike in gout, no negatively birefringent needle-like crystals were seen ([Fig. 1]).
Fig. 1 Hematoxylin and eosin-stained sections showing degenerated fat surrounded by mild infiltrates of chronic inflammation and multinucleated foreign body giant cells.
Comments
Clinically, SFNN usually presents as indurated subcutaneous mass lesions. The child is usually asymptomatic at presentation with no significant past medical history or findings upon physical examination (as it was the case here).
The etiology of SFNN is not certain, but an associated hypercalcemia can be seen in more than two-thirds of cases.[1]
[2]
Despite the name and predominant presentation in newborns, “SFNN” is not limited to newborn age as it can also be encountered later during infancy (our patient being 15 months old at the time of diagnosis as an example).[3]
The histologic findings of SFNN can be separated from those in gout nodules by noting that the deposited material in the latter shows birefringence under polarizing light. Gout is extremely rare in children with the rare exception of patients of Lesch–Nyhan syndrome, a metabolic disorder inherited in an X-linked mode that affects the metabolism of purines, the raw materials of deoxyribonucleic acid and ribonucleic acid. It is caused by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase, which is needed to recycle purines (the patient in this case was an otherwise asymptomatic girl and no birefringence was seen under polarized light).[2]
Conclusion
SFNN is not limited to the newborn age. The main differential diagnosis at the microscopic level includes gout skin nodules. Gout is extremely rare in children except in the rare metabolic disorder, Lesch–Nyhan nodules.
