THE ROLE OF PLATELET COUNT IN DECISION-MAKING FOR SUSPECTED GIANT CELL ARTERITIS CS Bouchard, MD, AZ Ahmad, MD, WC Park, MD, B Hayek, MD, S Blatt, MS4 Loyola University Medical Center, Chicago, IL Patient IDPlatelet Count (in thousands) GCA Biopsy Results 9518(-) 22375(-) 33419(-) 44440(-) 55454(+) 59464(+) Niederkohr et al devised a computer-based decision model that postulates that the thrombocytosis may identify GCA and that it’s absence may effectively it rule out. Our preliminary data supports a portion of Niederkohr et al’s model. Lack of high platelet count is effective; no thrombocytosis is associated with the exclusion of GCA. The data do not advocate ruling in GCA without biopsy. 66.7% of the patients with thrombocytosis had biopsies that proved the absence of GCA. Other laboratory tests, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are also necessary to consider. We are already spear-heading a Chicago-wide data collection effort to further examine this study. GCA: An Ophthalmic Emergency Methods Results Discussion No thrombocytopenia, No GCA References Thrombocytosis Results Thrombocytosis, High Suspicion for GCA Giant cell arteritis (GCA) is a primary ophthalmologic emergency. Vision loss is the predominant presenting symptom, and sequela, of this vasculitis. Vision loss may be permanent. This study clinically investigates the role of platelet count in the work-up of giant cell artertitis (GCA), as suggested by a recently published theoretical model. This is a retrospective case review analysis. Patient data will be included from , with final diagnosis confirmed by temporal artery biopsy. Patient laboratory data, in particular platelet count, will be applied to the “computer-based decision analytic model” and “pretest probability set” identified in the Niederkohr et al study: “Management of the Patient with Suspected Temporal Arteritis.” (Ophthalmology. Vol 112, No 5, May 2005). Inclusion criteria: We will identify patients who have been seen by the Department of Ophthalmology at Loyola University Medical Center for suspected GCA. Patients will have been either evaluated through inpatient services, as consultations to the Department of Ophthalmology, or as outpatients as emergency department consultations or ophthalmology clinic appointments. Patient data will be limited to the time period January 1, present. The suspicion for GCA will be defined by specific parameters: complaint of any of the following: headache, visual change, jaw claudication, scalp tenderness, arthralgia, myalgia, weight loss, and anorexia. Temporal artery biopsy must be performed within 1 week of initial presentation. Final diagnosis for each case must confirm or deny Giant Cell, or Temporal, Arteritis. If temporal artery biopsy is performed, final diagnosis must be based on surgical pathology. Of 27 cases, 6 (22.2%) patients with suspected GCA demonstrated thrombocytosis (platelets > 375,000). 2 of 6 subjects with GCA (7.41% of total) patients carried a final diagnosis of GCA, based on temporal artery biopsy. 17 (63.0%) of 27 cases without thrombocytosis did not have GCA. 1.Gabriel SE, et al. “The use of clinical characteristics to predict the results of temporal artery biopsy among patients with suspected giant cell arteritis.” J Rheumatol 1995; 22:93. 2.Haga HG, et al. “Cancer in association with polymyalgia rheumatica and temporal arteritis.” J Rheumatol 1993; 20: Jonasson F, et al. “Temporal arteritis: a 14-year epidemiological, clinical, and prognostic study.” Scott Med J 1979; 24: Kaiser PK, et al. The Massachusetts Eye and Ear Infirmary Illustrated Manual of Ophthalmology, 2nd Edition. Philadelphia: Saunders, Kanski JJ. Clinical Ophthalmology: A Systemic Approach. 5th Edition. Edinburgh: Butterworth Heinemann, Klein R, et al. “Large artery involvement in giant cell (temporal) arteritis.” Ann Intern Med 1975; 83: Lawrence RC, et al. “Estimates of the prevalence of arthritis an selected musculoskeletal disorders in the United States.” Arthritis Rheum 1998; 41: Niederkohr RD, et al. “Management of the patient with suspected temporal arteritis: a decision-analytic approach.” Ophthalmology 2005;112: Scott KR, et al. “Temporal artery biopsy technique: a clinico-anatomic approach.” Ophthalmic Surg 1991;22: Smetana GW, et al. “Does this patient have temporal arteritis?” JAMA 2002;287:92. ******************** Pre-test Probability With New Onset Visual Loss on Presentation Output Result Pre-test Probability No New Onset Visual Loss on Presentation Output Result 0.200% %(-): No TAB, No Tx; (+): Unil TAB 0.70%-3.000%(-): No TAB, No Tx; (+): Unil TAB % %(-): Bil TAB; (+): No TAB, Empiric Tx % %(-): Bil TAB; (+): No TAB, Empiric Tx (-): No thrombocytosis ( 375,000). Excerpt recreation of Figure 2, Niederkohr et al. “Management of the patient with suspected temporal arteritis.” Ophthal 2005;112: Platelets > 375,000 Platelets < 375,000 Acknowledgements: This work was supported in part by the Richard A. Perritt Charitable Foundation