A case of tauopathy with auditory agnosia and dysprosody diagnosed by [18F]PM-PBB3 tau PET scan

Abstract

Dear Editor, [F]PM-pyridinyl-butadienyl-benzothiazole 3 (PBB3), a propanol variant of the first tau positron emission tomography (PET) tracer, [C]PBB3, is reportedly a reliable tool for detecting tau fibrils in non-Alzheimer’s disease (AD) tauopathies [1]. Here, we report an antemortem tauopathy diagnosis by [F]PM-PBB3 imaging in a rare case with auditory agnosia and dysprosody. A 73-year-old right-handed woman, a former teacher, was referred to our hospital because she developed a gradual difficulty in hearing and unusual change in speech over the past 2 years. She had no significant medical history besides stomach cancer surgery at the age of 65 and no family history of similar diseases. Neurological examination, including tests for extrapyramidal symptoms, ataxia, cortical signs, or autonomic dysfunctions, revealed no abnormalities, except that she spoke like a foreigner who had just learned Japanese. Head magnetic resonance imaging (MRI) revealed mild right anterior temporal lobe atrophy (Fig. 1a), and singlephoton emission computed tomography showed hypoperfusion in the same area (Fig. 1b). Dopamine transporter scintigraphy indicated slightly reduced tracer uptake at the posterior right striatum (Fig. 1c). The patient did not provide consent for a spinal tap, but the plasma concentration of neurofilament light chain (14.25 pg/mL) measured by single-molecule array was high (normal range at our facility: less than 6 pg/mL). Neuropsychological evaluations revealed normal intelligence and no cognitive disturbance, based on standard assessment scores (Mini-Mental State Examination: 27; Wechsler Adult Intelligence Scale-III–V IQ 96; PIQ 112; Raven’s Colored Progressive Matrices: 28/36; Rey-Osterrieth Complex Figure Test-copy: 36/36; Rey-Osterrieth Complex Figure Test — 3-min delayed: 16.5/36; Wechsler Memory Scale-Revised Logical Memory Story A: immediate recall: 16/25; delayed recall: 13/25; Trail Making test A: 126 s, B:141 s, Word Fluency Category: 41/3 min, Initial letter: 21/ 3 min). She had no apraxia including bucco-facial apraxia. Her spontaneous speech was slow and dysprosodic, but her articulation was intact, indicating no dysarthria or apraxia of speech (AOS).We observed occasional phonemic paraphasia. Per the Japanese Standard Language of Aphasia test (Supplementary figure), she exhibited normal naming and word fluency. In auditory comprehension, she had difficulty recognizing spoken words, resulting in partially impaired repetition. Conversely, her written language comprehension was completely preserved. She could write sentences in both Kana and Kanji characters. Pure-tone audiometry and otoacoustic emissions were intact, but speech audiometry was impaired. Her auditory temporal resolution was reduced, and she had verbal auditory agnosia. In the auditory brainstem response, the auditory steady-state response and pure-tone threshold were normal; therefore, the auditory conduction pathway was not impaired. Moreover, environmental sound agnosia and amusia were observed. Consequently, we classified her symptoms as generalized auditory agnosia [2]. * Daisuke Ito [email protected]