An Unusual Case of Cerebral Venous Sinus Thrombosis With Negative D-dimer Mimicking Giant Cell Arteritis.

Cerebral venous sinus thrombosis (CVST) is a rare, potentially life-threatening condition that presents with variable symptoms such as headache, visual disturbance, and seizures, often mimicking an arterial stroke or intracranial lesion. Diagnosis can be challenging, and delays may result in severe outcomes. Although an elevated D-dimer may suggest CVST, a negative result does not exclude it. We report a rare case of extensive CVST initially treated as giant cell arteritis (GCA) due to unilateral temporal headache, elevated CRP, and a negative D-dimer. A 62-year-old man presented with acute left jaw pain progressing to a left-sided headache. He was initially treated for sinusitis but later developed temporal pain without scalp tenderness or visual disturbance. Referred for suspected GCA, he was started on high-dose prednisolone. CT imaging suggested possible left sigmoid sinus thrombosis, and although his D-dimer was negative, a CT venogram confirmed extensive thrombosis involving the left transverse, sigmoid, and internal jugular veins, with partial extension into the superior sagittal sinus. Thrombophilia screening revealed a positive lupus anticoagulant, and long-term anticoagulation with warfarin was initiated. This case highlights the need to consider CVST alongside GCA in patients over 50 presenting with temporal headache and jaw pain. A negative D-dimer does not rule out CVST, and a significant thrombus burden may exist despite negative results. Elevated CRP levels can occur in CVST and may be associated with a poorer prognosis, while testing for acquired thrombophilia can help determine the appropriate duration of anticoagulation in unprovoked cases.