Obstructive Raynaud's syndrome can be differentiated from vasospastic Raynaud's syndrome by the:

D. Digital blood pressure measurement.

DISCUSSION: Patients with obstructive Raynaud's syndrome have fixed palmar and digital arterial lesions with a decrease in digital blood pressure at rest. In contrast, patients with vasospastic Raynaud's syndrome have normal digital arteries at rest and normal digital blood pressure. Therefore the only test that differentiates the two conditions is measurement of digital blood pressure. The ice water and digital hypothermic challenge tests both test for the presence of Raynaud's syndrome, but do not differentiate the spastic from the obstructive type. The presence or absence of antinuclear antibodies does not determine whether obstruction is present, although it is true that many patients with obstructive Raynaud's syndrome will have a positive test.