Histiocytosis in Injecting Drug Users

The goal of this observational study is to describe a new disease condition of histiocytosis related to injecting drug use, its preconditions, symptoms, signs, findings, and prognosis in a detailed and systematic patient series in one referral center. The main question[s] it aims to answer are:

* to find specific histologic features in different tissues to help the differential diagnosis from other histiocytoses * to describe the value of chitotriosidase activity to screen this condition * to describe the value of various tissue biopsies in confirming the diagnosis * to describe the nature of polyvinylpyrrolidone accumulation in tissue macrophages by novel special microscopic techniques * to find new tandem mass spectrometry methodology to prove polyvinylpyrrolidone accumulation in macrophages * to show that polyvinylpyrrolidone treatment activates macrophages to histiocytes and causes povidone accumulation within the cells in in vitro experiments * to evaluate the pathology of macrophage activation to histiocytes by transcriptomics

The patient history will be collected from the data produced by follow-up of cases followed up in a single center. A subgroup of participants will be given an opportunity to sign informed consent to give access to/donate blood and tissue samples to search for techniques to prove polyvinylpyrrolidone storage within histiocytes, and to search for transcriptomics signal(s) in histiocytes.

Researchers will compare blood and tissue samples from the biobank as controls.