MT3. Joint Pain (MTz & Team) - Material with Answers.docx

Introduction This tutorial is based around the clinical and laboratory diagnosis of a patient presenting with joint pain. In preparation, you should have completed the virtual ELISA exercise at: https://www.hhmi.org/biointeractive/immunology-virtual-lab Please work through the material in pairs. Aft...

Introduction This tutorial is based around the clinical and laboratory diagnosis of a patient presenting with joint pain. In preparation, you should have completed the virtual ELISA exercise at: https://www.hhmi.org/biointeractive/immunology-virtual-lab Please work through the material in pairs. After around 20 minutes your tutor will review the answers with the group. Aims To consolidate knowledge of immunoassay methodology To consider the presentation and diagnosis of inflammatory joint disease Learning objectives You should be able to: Describe the features of inflammatory joint disease List a differential diagnosis for acute monoarthritis Draw/ list the key steps in an ELISA experiment Comment on the technical validity of an ELISA experiment Comment on the significance of positive CCP antibody Describe the presentation, based on the history, appearances and the examination findings Answer: the features of recent-onset heat, swelling, redness and pain are consistent with acute inflammation of the knee. The descriptive term would be ‘acute monoarthritis’ as only one joint is inflamed Thinking back to the ‘introduction to diseases of the musculoskeletal system’ lecture, list some differentials for this presentation. Against each, discuss some pros and cons for the possibility Differential In favour Against Answer: Differential In favour Against Septic arthritis Common cause for monoarthritis in young adults No fever or systemic upset Crystal arthropathy Can cause monoarthritis Young with no risk factors Haemarthrosis Can cause monoarthritis No history of trauma, nil to suggest clotting disorder Acute osteoarthritis Can cause monoarthritis Very young Rheumatoid arthritis Young woman, history of joint pain Usually presents with multiple rather than single joint involvement Psoriatic arthritis Young woman, history of joint pain No history of psoriasis (although joint problems can predate skin involvement), usually presents with multiple joints Sarcoidosis Can cause monoarthritis Rare, no other features of the disease NOTE this is not an exhaustive list; discussion is encouraged, and students should be directed to do their own research independently if unsure Draw and briefly the KEY steps in the ELISA assay from this point Answer -The optical density is then read and curve control values are plotted. The optical density of the patient well is then used to derive the CCP antibody concentration. This is a big source of confusion for students – please use a whiteboard or similar to go through the steps. [CHART] Regarding the control results, comment on the technical validity of the assay Answer: The kit controls are pre-supplied; the internal quality control sample is provided by the laboratory and run with every assay. Failure of any control sample to fall within the acceptable range may invalidate the assay and should prompt investigation. In this case, all controls are within the expected range, therefore the run is technically valid and may be accepted. The optical density for the patients sample well is 0.576. Use the CCP standard curve to estimate the CCP antibody concentration in the patient’s sample, or you could calculate the value using the curve equation. Answer: using the equation the patient has 103.05 U/ml CCP The test is considered to be positive at 10 units/ ml. What is your interpretation of this result in the context of the patient presentation, and what should happen next? Answer: Positive CCP antibody in the setting of joint inflammation is strongly predictive for rheumatoid arthritis. She should be referred urgently to Rheumatology to consider immunomodulation, which should be started before joint damage ensures. Note that the presentation with monoarthritis is a bit unusual however, so the full clinical picture and other test results will be important to consider.