Evaluation of Non-Inflammatory Nodule Formation After Low-Dilution Calcium Hydroxyapatite Applications: A 4-Case Report Series

Abstract

 The use of calcium hydroxylapatite (CaHA) for collagen biostimulation in the face and neck is highly prevalent. While CaHA demonstrates an excellent safety profile with a lower incidence of severe inflammatory responses compared to other biostimulators like poly-L-lactic acid (PLLA), the development of post-application nodules represents an episodic clinical challenge. This retrospective case report series evaluates 4 specific clinical cases from an independent, real-world evidence study in Brazil where female patients developed non-inflammatory nodules following subdermal applications of CaHA at a low dilution ratio (1:1) in the cervical regions. Nodule formation was observed uniformly 30 days post-treatment across all 4 reported cases. The clinical presentation was strictly non-inflammatory, characterized by a lack of erythema, pain, heat, or localized edema. While hyperdiluted forms (1:2 to 1:4) drastically reduce cohesivity and optimize tissue integration, low-dilution (1:1) applications are associated with an increased propensity for focal product aggregation. Due to the small sample size of this series, larger multi-center studies are required to formulate definitive conclusions.