Prognostic value of olfactory nerve damage measured with thallium-based olfactory imaging in patients with idiopathic olfactory dysfunction

Abstract

Idiopathic olfactory disorder is resistant to treatment, and the recovery time is long. This study investigated the prognostic value of the migration of nasally administered thallium-201 to the olfactory bulb (thallium migration to the OB), a measure of olfactory nerve damage, in patients with idiopathic olfactory disorders. Twenty-four patients with idiopathic olfactory disorders were enrolled in the study (7 women and 17 men; aged 23–73 years). We retrospectively analyzed potential prognostic markers in subjects who underwent thallium-based olfactory imaging with the nasal administration of thallium-201 before conventional treatment with the Japanese herbal medicine tokishakuyakusan and compared those data with the prognosis. Log-rank tests were performed to assess the relationship between thallium migration to the OB (<4.6% [low] vs. ≥4.6% [high]; data dichotomized at the optimal cutoff value) and the duration until recovery of the odor recognition threshold determined by a standard olfactory function test (T&T olfactometry) after the treatment. Upon statistical analysis, we found that high thallium migration to the OB was significantly correlated with better prognosis in patients. Our results suggest that patients with intact olfactory nerve fibers could be selected using thallium-based imaging for the long-term follow-up of olfactory dysfunction.

Nasal thallium‐201 uptake in patients with parosmia with and without hyposmia after upper respiratory tract infection

“…The OB volume was significantly larger in the parosmia group than in the parosmia and hyposmia group (Fig. , p = 0.029); however, the mean OB volume in both groups (31.2 mm 3 in the parosmia group and 22.6 mm 3 in the parosmia and hyposmia group) was lower than the normal value in healthy subjects (≥58 mm 3 for <45 years; ≥46 mm 3 for older subjects). The nasal thallium uptake ratio in the olfactory cleft was significantly correlated with T&T odor recognition thresholds (Fig.…”

“…In Japan, T&T olfactometry (Daiichi Yakuhin Sangyo, Tokyo, Japan) is a standard technique for estimating the olfactory thresholds; the normal odor recognition threshold score of each nostril is ≤2.0. The olfactory severities were categorized according to the mean T&T recognition thresholds, and the patients were diagnosed with anosmia when the T&T recognition thresholds were ≥5.6 . Each odorant was dissolved in mineral oil to form a graded series of concentrations and was then applied liberally on blotting papers followed by presentation to the patients using T&T olfactometry.…”

Thallium-201 Imaging in Intact Olfactory Sensory Neurons with Reduced Pre-Synaptic Inhibition In Vivo

“…With the use of in vivo imaging via SPECT-CT, we demonstrated that thallium-201 migration to the axon terminals of olfactory sensory neurons was increased under reduced inhibitory input from damaged olfactory bulb interneurons, following nasal administration of rotenone in rats. Decreased thallium-201 migration rate to the olfactory bulb predicted a poorer prognosis for patients with idiopathic olfactory dysfunction [23]. Patients with idiopathic olfactory dysfunction and decreased thallium-201 migration rate to the olfactory bulb may be at high risk for pre-symptomatic idiopathic Parkinson's disease because the overexpression of dopaminergic interneurons in the olfactory bulbs of patients diagnosed with idiopathic Parkinson's disease has been demonstrated [24].…”

Pharmacoimaging of Blood-Brain Barrier Permeable (FDG) and Impermeable (FLT) Substrates After Intranasal (IN) Administration

“…(20–22) Higher migration rates to the OB were found in subjects with normal olfactory thresholds compared to patients with impaired olfaction because the tracer migration was associated with intact olfactory nerve fibers. Although these studies do not report on the use of imaging, and specifically PET imaging, as a tool for the evaluation of the PK properties of IN dosage forms, they support the feasibility and tolerability of human imaging after IN administration of radiotracers and suggest the direct role of the olfactory neurons in the transfer of materials within the nasal mucosa.…”