We present a patient who had a diagnosis of probable dementia with Lewy bodies (DLB) according to consensus guidelines.1 Rapid eye movement (REM) sleep behavior disorder (RBD) was part of his clinical spectrum. Unrelated to his neurodegenerative process, our patient had severe hearing impairment and was a native signer in American Sign Language (ASL)—his main source of linguistic communication. As part of his dream‐enactment behavior, he would fluently sign rather than verbalize in spoken language. This manifestation of RBD has not been previously reported and allows for discussion of the similar neural systems that underlie both spoken and signed language.
Case Report
We present the case of a 71‐year‐old, right‐handed man who had childhood‐onset, severe hearing impairment with a more recent history, since age 67, of progressive parkinsonism. Motor manifestations included bilateral rigidity, bradykinesia, and rest tremors. Early in the disease course, he developed dementia and psychosis with well‐formed “Lilliputian” visual hallucinations, which were treated with neuroleptic medications. His psychosis has progressed to include delusions (including Capgras delusion, insisting his wife was an imposter, and that the Movement Disorders fellow was Pablo Escobar) and aggressive outbursts, necessitating ongoing treatment with neuroleptic medications.
His prior neuroleptic treatments had included risperidone and quetiapine, both of which significantly worsened his motor symptoms. Quetiapine was withdrawn and pimavanserin was initiated with recurrence of his aggressive behavior, which was then quelled with olanzapine. Rivastigmine was added to further control visual hallucinations. His response to carbidopa‐levodopa has not been robust.
During sleep, he displayed dream‐enactment behavior, including punching and kicking (occasionally inflicting minor injuries on his bed partner). In addition, he would fluently sign in ASL. The situation in his dreamscape could be deduced by his signing.
Discussion
DLB1 is a synucleinopathy and is the second most common cause of neurodegenerative dementia. Aside from the core features that define this condition, there are supportive features, such as RBD, which increase diagnostic sensitivity. RBD was reported in 96% of patients with DLB in a polysomnographic (PSG) study.2 On PSG, which is needed to definitively diagnose the condition, RBD manifests as increased electromyographic tone with dream‐enactment behavior during REM sleep.3 In a given patient, parkinsonism may limit mobility during wakefulness, but the movements associated with RBD can be faster, stronger, and smoother; and speech may be more comprehensible.4 It has been suggested that the movement generated by the motor cortex can bypass the abnormal extrapyramidal system to continue as the corticobulbar and corticospinal tracts.4
Without PSG for definitive diagnosis, other parasomnias and nocturnal events must be included in the differential diagnosis of RBD. Parasomnias of slow‐wave sleep, such as confusional arousals or night terrors, should be considered.3 RBD and non‐REM parasomnias can be clinically differentiated. Patients with non‐REM parasomnias tend to be amnestic to the event and are difficult to arouse from sleep during the behavior.5 In RBD, the patient may recall a vivid dream and is more easily awoken, which resolves the behavior.5 The possibility that the patient is actually awake and responding to hallucinations should be considered. However, according to the patient and his bed partner's recollection, our patient is asleep while signing, and he can recall the vivid dream associated with the actions. Given the clinical history and that RBD is quite prevalent in DLB, the described behavior is most likely a manifestation of RBD.
Fluent signing of ASL has not been reported as a manifestation of RBD. Sign languages, like spoken languages, have linguistic structure, established vocabularies, and grammatical principles. We have evidence for a similar neural substrate underlying the expression and comprehension of both signed and spoken language. For example, a similar deleterious effect on expressive or receptive language (spoken or gestured) can be expected from an insult to the dominant hemisphere of the brain. Furthermore, functional imaging studies show left hemispheric perisylvian cortex activation—in Broca's area for expression and Wernicke's area for comprehension of signed language.6 We also know that nonlanguage hand gestures, as opposed to language hand gestures (emblems), have different neural substrates. This is supported by functional imaging studies showing that signers engage left‐lateralized language centers when viewing sign language, whereas nonsigners (who would interpret sign language as nonspecific gestures) only activate areas attuned to perceiving movement7 (such as the premotor cortex and inferior parietal lobule).8 Sign language is equivalent to spoken language (and different from nonspecific hand gestures) in terms of central processing (with the exception of the need for auditory cortex to perceive spoken language). Thus, in a patient with RBD who is native in ASL, it is reasonable to expect that hand signing would replace the expected abnormal vocalizations.
Our patient represents a classic case of DLB. As a native in ASL, he provides a unique manifestation of RBD. In addition, this case further supports the concept of similar neural substrates involved in both signed and spoken language.
Author Roles
1. Research Project: A. Conception, B. Organization, C. Execution; 2. Statistical Analysis: A. Design, B. Execution, C. Review and Critique; 3. Manuscript Preparation: A. Writing the First Draft, B. Review and Critique.
J.M.: 1A, 3A
C,L.: 3B
C.S.: 3B
Disclosures
Ethical Compliance Statement: We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines.
Funding Sources and Conflicts of Interest: The authors report no sources of funding and no conflicts of interest.
Financial Disclosures for previous 12 months: Dr. Margolesky reports no sources of funding and no conflicts of interest. Dr. Luca is a consultant for Medtronics. Dr. Singer has received grants from from Cynapsus, Adamasa, Allergan, Huntington Study Group, Parkinson Study Group.
Relevant disclosures and conflicts of interest are listed at the end of this article.
References
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