Making Sense of Late Tissue Nodules Associated With Hyaluronic Acid Injections.

The group believe that filler, pathogens and inflammation are all involved in DTNs and that DTNs most likely are infection initiated with a variable immune response. Injected filler may incorporate surface bacteria, either a commensal or a true pathogen if the skin barrier is altered. The initially High molecular weight HA (HMWHA) filler is degraded to Low molecular weight HA (LMWHA) at the edge of the filler. Commensals positioned within the filler bolus may be well tolerated until the filler is degraded and the commensal becomes visible to the immune system. LMWHA is particularly inflammatory in the presence of any local bacteria. Commensals may still be tolerated unless the immune system is generally heightened by viraemia, or vaccination. Systemic pathogenic bacteraemia may also interact with the filler peripheral LMWHA, activating Toll Like receptors inducing DTN formation. Given this scenario, attention to practitioner and patient hygiene and early systemic infection treatment deserve attention. Classification and treatment systems were devised by considering each of the 3 factors of filler, inflammation, and infection separately.