Described are methods for detecting and/or diagnosing systemic sympathetic nervous system dysfunction or disease in a subject. One embodiment comprises using a topical apraclonidine eye drop to detect an ocular condition indicative of sympathetic dysfunction or disease in a subject with Guillain-Barré syndrome (GBS). Embodiments can be used to detect and/or diagnose systemic sympathetic nervous system dysfunction or disease early, prior to development of substantial symptoms. Embodiments can also be used to unmask either bilateral ptosis or bilateral Horner's syndrome in GBS patients with the application of the drop to one eye. Also described are dosage forms suitable for use in the methods described herein. The dosage forms comprise an alpha receptor agonist with alpha-1 receptor activity. In one embodiment the dosage form comprises apraclonidine packaged as a single-use eye drop.
