Thrombocytosis in temporal arteritis rising platelet counts: a red flag for giant cell arteritis.

OBJECTIVES To determine whether early recognition and detection of thrombocytosis in patients with giant cell arteritis can help secure an earlier diagnosis, and whether it can help differentiate cases of arteritic optic neuropathy from other forms of optic neuropathy. METHODS Medical and ophthalmologic records from 1993 to 1998 of the authors' patients with biopsy-proven temporal arteritis versus the authors' patients with nonarteritic anterior ischemic optic neuropathy and idiopathic demyelinating optic neuritis were prospectively collected. Past and present blood analyses were collected, and platelet counts were compared between patients with giant cell arteritis and control populations. This was done to determine whether thrombocytosis could help with the diagnosis and differentiation of these different disease states. RESULTS There was a significant difference in the frequency of thrombocytosis in patients with giant cell arteritis (13 out of 19 patients), with or without arteritic ischemic optic neuropathy, as compared with those with nonarteritic anterior ischemic optic neuropathy (zero out of 30 patients), idiopathic optic neuritis (zero out of 26 patients), and healthy age-matched controls (one out of 22 control subjects). This difference was especially helpful in patients whose sedimentation rates were within the normal range (adjusting for age). Also noted was the finding that the rise in the platelet counts was not acute, but rather it was a slow gradual increase for approximately 12 months before the onset of significant systemic or visual symptoms. CONCLUSION Thrombocytosis should be considered an important marker in patients being referred for evaluation of ischemic optic neuropathy, diplopia, amaurosis fugax, headache, or even generalized malaise. Westegren sedimentation rates <50 mm/hr are often erroneously viewed as nondiagnostic or equivocal in the elderly and just followed. An over-the-phone review of patients' sedimentation rates, complete blood counts, and platelet counts can lead to expedited evaluation and treatment of patients who may be at high risk of visual loss from temporal arteritis. Thrombocytosis should lower a physician's threshold to acutely treat patients for possible arteritic ischemic optic neuropathy until the disease is definitely ruled out.