Recently, I was consulted to the neonatal ICU to evaluate a newborn with red, indurated, fluctuant plaques on the back. I had no doubt that this was a classical case of subcutaneous fat necrosis of the newborn (SCFN). A biopsy demonstrated a neutrophilic panniculitis without crystals – a tissue gram stain and culture confirmed the diagnosis of Staphylococcal panniculitis (mimicking neutrophilic SCFN). Humbled again.
Ricardo-Gonzalez et al just published their series of neutrophil-rich SCFN based on their index case of a 4 day-old girl with erythematous, firm, centrally fluctuant nodules. Purulence was noted when the biopsy was performed. The clinical team’s first impression was that this was an infection. The biopsy demonstrated a lobular neutrophilic panniculitis with fat necrosis and needle-shaped clefts. Stains for microbes were negative, as were cultures. Transient hypercalcemia was noted. The lesions resolved over 6 months. The authors reviewed 13 cases of SDFN from their institution; two of these cases displayed > 75% neutrophils in the infiltrate. Importantly, all 13 demonstrated needle-shaped clefts. In their review of 124 cases from the literature, ten were noted to have neutrophilic infiltrates, but none of these cases were neutrophil predominant. Although the histologic differential diagnosis could include subcutaneous Sweet syndrome or alpha-1 antitrypsin deficiency, neither of these would display the needle-shaped clefts. The presence of neutrophils presumptively correlates with early lesions of SCFN prior to becoming more granulomatous (1).
Clinically, my case looked exactly like this (and every other) neonate with SCFN – the key difference being that needle-like clefts were not observed in the context of a lobular neutrophilic panniculitis histologically. Sometimes what looks like an infection might actually be an infection! Based on my experience, do not diagnose SCFN unless you can demonstrate those needle-like clefts. A simpler way to do that may be by fine needle aspiration, as recently described by Schubert et al (2).
- Ricardo-Gonzalez RR, et al. Neutrophil-rich subcutaneous fat necrosis of the newborn: A potential mimic of infection. J Am Acad Dermatol 2016; 75: 177-85.
- Schubert PT, et al. Fine-needle aspiration as a method of diagnosis of subcutaneous fat necrosis of the newborn. Pediatr Dermatol 2016; 33: e220-1.