Its main mechanism of pathogenesis is vascular invasion which causes thrombosis, which can lead to tissue necrosis. Ki16198 septic arthritis that is culture negative and refractory to empiric antibiotics, particularly in an immunocompromised Ki16198 individual. It also shows the importance of a thorough social history and adequate tissue specimens for culture. Keywords: mucormycosis, Apophysomyces, mould, methenamine silver staining, septic arthritis, amputation == Introduction == Mucormycosis (zygomycosis) is a rare fungal infection caused by moulds in the order Mucorales. These moulds are ubiquitous in nature and can be found in soil, decaying wood and other organic matter (Neblett Fanfairet al., 2012). They can cause a variety of infections, with skin and soft tissue infections being a common clinical manifestation. These infections can be quite devastating, causing complications such as tissue necrosis and necrotizing fasciitis, especially in immunocompromised individuals (Neblett Fanfairet al., 2012). There is substantial morbidity and mortality associated with these infections (Vaeziet al., 2016). Apophysomycesspecies are an unusual cause of mucormycosis, accounting for 3 % of cases reported in the literature (Echaizet al., 2013). Cases involving this mould are usually associated with penetrating trauma, particularly after natural disasters. The speciesApophysomyces trapeziformiswas implicated in cases of necrotizing soft tissue infections following the tornado that ravaged Joplin, Missouri, in 2011 and the Indian Ocean tsunami in 2004 (Gomeset al., 2011; Neblett Fanfairet al., 2012). Mucoraceous moulds rarely cause septic arthritis, with only a few case reports described (Mostazaet al., 1989; Parra-Ruizet al., 2008). In this report, we present a patient with multiple myeloma who presented with persistent septic arthritis of the left knee, who ultimately was found to haveA. trapeziformisgrowing from his synovial cultures. This case illustrates the importance of obtaining a thorough social history and adequate tissue samples for culture, as well as considering fungal infection in cases of septic arthritis where cultures are negative for bacterial growth and empiric antibiotic therapy is ineffective. == Case report == A 62-year-old African American male with a history of multiple myeloma previously treated with pamalidomide presented to a Veterans Affairs (VA) hospital with a 3 day history of progressive pain and swelling in the left knee as well as fever. X-ray of the left knee showed joint effusion. He underwent an arthroscopic incision and drainage (I&D) of the left knee, which revealed a cell count of 50 250 white blood cells (WBCs) cm. Routine synovial cultures were negative for bacteria, and there were no crystals present in Ki16198 the fluid. The patient was started on vancomycin 1 g daily, pipercillin-tazobactam 3. 375 Ki16198 g every 6 h and clindamycin 600 mg every 8 h prior to the procedure, and was continued on them while in the hospital. He was discharged on oral ciprofloxacin 500 mg twice a day and doxycycline 100 mg twice a day. Five days after discharge, he presented back to the same VA hospital with recurrence of left knee pain and swelling. Repeat I&D again showed purulent fluid with a cell count of 74 663 WBCs cm. Again, the synovial cultures were negative for bacteria (of note, he was started on vancomycin 1 g daily and pipercillin-tazobactam 3. 375 g every 6 h prior to the procedure once again). Synovial fungal and acid fast bacilli cultures were also sent at this time, and those were negative as well. The rheumatologist also evaluated the patient, and determined that the patient did not have rheumatoid arthritis (serum rheumatoid factor and serum cyclic citrullinated peptide antibody were both negative). The patient was treated empirically for septic arthritis again, first with vancomycin and pipercillin-tazobactam, and then was discharged on intravenous antibiotics with vancomycin 1 g daily and CD14 ertapenem 1 g daily for a total of 6 weeks of therapy. The patient was also treated empirically for gout, despite no crystals, first with colchicine 0. 6 mg daily for 7 days, and then with a Ki16198 prednisone taper (40 mg daily for 5 days, 20 mg daily for.