Delayed skin test reaction to injectable collagen implant (Zyderm). The histopathologic comparative study

Ten cases of persistent positive test site responses to enzyme-digested purified bovine collagen solution (EPC; Zyderm Collagen Implant) were reviewed. Specimens were stained with hematoxylin and eosin, Gomori's trichrome, colloidal iron, elastic van Gieson, Snook 's reticulum, and polarized light. These granulomatous-like reactions were compared with cases of granuloma annulare, hypertrophic scarring, keloids, and rheumatoid nodules. These studies make it possible to differentiate a normal EPC implant from normal reticular dermis. The granulomatous reaction around the EPC implant can be differentiated from granuloma annulare, scars and keloids, and rheumatoid nodules. It is our conclusion that the granulomatous material is probably a combination of EPC and small amounts of altered human collagen.