Prognostic value of olfactory nerve scintigraphy by per-nasal Tl-201 administration in patients with impaired sense of smell

Objectives For patients with hyposmia, there are no established prognostic markers. We have reported that olfactory nerve scintigraphy by per-nasal Tl-201 administration can visualize the olfactory nerve damage in patients with hyposmia. The aim of this study was to assess whether olfactory nerve scintigraphy can be a prognostic marker for patients with olfactory disturbance.

Methods 30 patients with hyposmia (15 males, aged 23-71) were enrolled in the study. The cause of hyposmia were chronic rhinosinusitis (n=7), upper respiratory tract infection (n=4), head trauma (n=7), and idiopathic (n=12). Before treatment patients were administered 18-37 MBq of Tl on the olfactory mucosa. 24 hr later, SPECT/CT was performed. CT image from SPECT/CT was fused with MRI image that obtained separately, then SPECT/MRI fused image was generated. On the SPECT/MRI coronal and sagittal fused images, region of interests were set to cover the area of Tl administered on the olfactory mucosa and on the olfactory bulb. The % uptake of the Tl of the olfactory bulb (U) was calculated as: U = 100 (counts of the olfactory bulb / counts of the olfactory mucosa). Odor recognition thresholds were measured by T&T olfactometry, a standard means of measuring olfactory threshold in Japan, before and after treatment. Improvement in T&T odor recognition threshold was judged according to the criteria of the Japanese Rhinologic Society.

Results The duration until recovery of odor recognition was significantly shorter in patients with high U (>4.6%) (Log-rank test, p=0.012). Odor recognition recovery within 1 year after treatment was observed in 37% of patients with high U, but none of patients with low U.

Conclusions Tl-201 transport from olfactory mucosa to olfactory bulb could be a marker of predicting the prognosis in patients with olfactory disturbance.