The histology best fitted a diagnosis of nodal marginal zone lymphoma with plasmacytic differentiation, with a diagnosis of lymphoplasmacytic lymphoma being less likely because of the presence of residual but disrupted follicles. A right level V cervical lymph node was excised and showed a diffuse infiltrate of intermediate-sized lymphoid cells, many of which exhibited plasmacytoid morphology. Immunohistochemistry showed positive staining with CD20, MUM-1 and BCL2, but no staining with CD10, Bcl6, CD23 or Cyclin D1. Ki67 staining was low to moderate. The histology best fitted a diagnosis of nodal marginal zone lymphoma with plasmacytic differentiation, with a diagnosis of lymphoplasmacytic lymphoma being less likely because of the presence of residual but disrupted follicles. The lymph node biopsy and bone marrow G-CSF aspirate both agreed with a diagnosis of nodal marginal zone lymphoma. While MYD88 L265P mutation analysis was positive, it has been shown that nodal marginal zone lymphoma can be sometimes associated with this mutation.5 Differential diagnosis The first issue was the differential diagnosis of polyarthropathy: infective, autoimmune, gout or pseudogout. Purpureaside C The differential was quickly limited to an infective polyarthropathy after a positive gram stain from synovial fluid and associated raised inflammatory markers. The the most common organism isolated in septic arthritis is usually (44%) as well as others include species and septic arthritis. This was further changed to ceftriaxone 1?g intravenous one time per day as per local hospital guidelines after the result of and this was increased to 2?g after worsening joint symptoms. Treatment continued for 1?month until Purpureaside C symptoms resolved. The second 2 weeks of treatment were given on an outpatient parenteral antimicrobial therapy basis. He was treated with 6 cycles of rituximab and bendamustine for the lymphoma, with a total remission on the end of induction CT scan and decrease of his paraprotein. Rituximab maintenance is usually planned to consolidate the response. End result and follow-up His joint symptoms began to handle, the CRP became normal and he was discharged. He remains under follow-up at the haematology medical center. Conversation This case highlights the important aspect that diagnosis of one condition can lead to diagnosis of another. In this patients case, it was his weakened immune system from your nodal marginal zone lymphoma which led to his presenting symptoms of polyarthropathy as a result of primary meningococcal arthritis. In the literature, there is one case of a 74-year-old man presenting with meningococcal meningitis and arthritis and was found to have an underlying Waldenstr?ms disease.4 He had a recurrence of meningococcal arthritis 8?years later. There is also a case statement of HIV being diagnosed after the patient presented with meningococcal arthritis.7 These Purpureaside C cases highlight the importance of screening for an underlying impaired immune response in patients presenting with rare conditions such as meningococcal arthritis. Learning points In a case of septic arthritis, early acknowledgement and treatment is required in order to prevent joint destruction. Meningococcal contamination may rarely present as septic arthritis in the case of invasive meningococcemia, but main meningococcal arthritis is usually rarer. Early acknowledgement of main meningococcal arthritis is usually important in order to prevent the risk of dissemination of the disease. Consider the possibly of an underlying health problem, for example, an immune defect, in those presenting with meningococcal arthritis. A high serum total protein should prompt Purpureaside C investigation for HIV myeloma or lymphoma. Footnotes Contributors: GAJH published the article with JT and AM amending it. JT provided haematology input. Funding: This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Competing interests: None.