Rapid cytologic diagnosis of subcutaneous fat necrosis of the newborn.

Subcutaneous fat necrosis of the newborn is a rare self-limited panniculitis that classically presents within the first few weeks of life. The diagnosis is typically clinical, but some cases require skin biopsy with hematoxylin and eosin stain for confirmation. We report a previously undocumented rapid diagnostic protocol that involves collecting a small amount of exudate from a suppurative lesion, placement onto a slide without fixation, and simply viewing the material under a microscope. This novel and practical method of diagnosis reveals doubly refractile crystals diagnostic of subcutaneous fat necrosis without a biopsy, which may be helpful for rapid diagnosis or use in low resource settings.