Fluorodeoxyglucose F18 PET in progressive emotional dysprosody

While the left hemisphere is important for semantic and grammatical language, the right hemisphere appears to be important for prosody.

In this report we describe a patient who presented with progressive emotional dysprosody in which Cortex-ID analysis of her fluorodeoxyglucose F18 PET (FDG-PET) scan revealed an area of focal hypometabolism in right superior medial frontal lobe.

Case report.

A 64-year-old right-handed, US-born, bilingual (English, Spanish) woman employed as a translator in Spain presented with a 4-year history of progressive difficulty expressing herself emotionally. Initially, she had difficulty speaking Spanish. While she previously was regarded as an excellent storyteller, she could not convey emotion through her stories, which became “robotic” in her words. Subsequently, she lost her Spanish accent. As a translator, she prided herself on the fact that no one knew she was born in the United States because her accent was flawless. She was fluent in Spanish prior to the age of 18. She also previously enjoyed singing but reports that she was no longer able to sing because her singing voice became flat and she was unable to hold a tune. Neurologic examination was unremarkable. She received a score of 37/38 on the Kokmen Short Test of Mental Status.¹ One of the behavioral neurologists examining her (D.A.D.), a fluent Spanish speaker, noticed the marked change in her ability to communicate in Spanish compared to English (only a limited portion of the examination was performed in Spanish). She sang happy birthday with mild difficulty but her husband noted it did not sound anything like how she previously would have sounded. When the examiner asked her to repeat a sentence in either a happy or angry tone, she spoke more monotone in Spanish than in English. She was able to recognize the examiner's emotional tone, but this was tested only in English. She underwent detailed evaluation by a speech language pathologist (E.A.S.). She had no verbal or nonverbal oral apraxia. Auditory comprehension was tested with the Token Test Part V.² She scored 22/22, showing normal performance. She demonstrated normal naming and her picture descriptions were characterized by normal grammar and syntax with no delays for word retrieval and no paraphasias. Her reading and writing were normal. Formal neuropsychological analysis revealed normal learning and memory scores on the Rey Auditory Verbal Learning Test. Trails A and B were performed in 21 and 41 seconds respectively without errors. She scored 56/60 on the Boston Naming Test. She named 23 animals in a 1-minute period and 44 words beginning with P, T, C, and S. Visual spatial function tested with the Rey-Osterrieth Complex Figure was normal. Brain MRI completed elsewhere was formally reviewed and revealed only mild generalized cerebral volume loss without any particular lobar distribution. Cortex ID analysis of her FDG-PET (GE Healthcare, Waukesha, WI) is displayed in the figure.

Figure. Fluorodeoxyglucose F18 PET demonstrates focal marked hypometabolism in the superomedial right frontal lobe.

Discussion.

Our patient's clinical presentation, focal hypometabolism in the right supplementary motor area, and MRI without focal deficits would suggest a neurodegenerative disorder affecting primarily the right hemisphere language functions. The involvement of the right hemisphere is consistent with an earlier report.³ Our findings suggest that the medial superior frontal lobe is the neuroanatomic correlate of emotional prosody as previously described⁴ and is consistent with the notion that right hemisphere lesions are associated with impairment of affective speech.^5–7

We recently reported that the neuroanatomic correlate of progressive apraxia of speech is the superior lateral premotor cortex or supplementary motor area.⁸ However, it has remained unclear whether it is the right, left, or bilateral superior premotor cortex. Given the absence of apraxia of speech in this subject, it appears that the neuroanatomic correlate of apraxia of speech is more likely the left superior premotor cortex or requires both left and right superior premotor cortices to be involved.

One limitation of our article is that the findings may not be applicable to those who speak 1 language since our subject is bilingual.

While primary progressive aphasia has been categorized according to clinical presentation and underlying pathology, primary dysprosody of speech appears to be a distinct clinical entity. Our case highlights that PET imaging provides a new means of diagnosing this rare disorder.