We identified 67 patients with PSPS, CBS or MSA who had volumetric MRI as well as FDG-PET imaging. Midbrain volume was measured and expressed as a percentage of total intracranial volume. Two independent, blinded specialists rated the 鈥榩imple sign鈥?on FDG-PET as 鈥榓bsent鈥? 鈥榩ossible鈥?or 鈥榙efinite鈥? Midbrain volumes were compared across these groups and reliability assessed with the kappa statistic. Sensitivity and specificity were calculated using CBS and MSA patients as controls.
Midbrain volume was decreased in the 鈥榙efinite鈥?group compared to the 鈥榓bsent鈥?and 鈥榩ossible鈥?groups (p聽=聽0.0036). Inter-rater reliability for the pimple sign was high (魏聽=聽0.90). A 鈥榙efinite pimple sign鈥?had a high specificity (100%) but low sensitivity (29%) for PSPS, whilst the presence of a possible or definite sign had a sensitivity of 79%.
The 鈥榩imple sign鈥?of PSPS is associated with midbrain atrophy, and may be helpful in differentiating PSPS from CBS and MSA.