A diagnostic apparatus for testing nerve pathways through skin sensitivity, including a handle, a support assembly mounted to the handle, an axle affixed to the support assembly, a removable wheel having an axle hole adapted to receive the axle, the wheel having a plurality of tines extending radially therefrom, the tines extending to form a point, and a retaining assembly for securing the wheel on the axle, the retaining assembly being movable relative to the axle to facilitate removal and replacement of the wheel; and a dispenser for dispensing the disposable wheels to facilitate easy replacement and prevent contamination of new wheels from handling.