By Heather Jeng
Usually, we SLPs in the SNF find ourselves reading clinical research within the field of speech-language pathology. This month, we’re taking an interdisciplinary perspective by checking out what some of our neurosurgeon & neuroscience colleagues have been focusing on regarding deep brain stimulation (DBS) and speech intelligibility.
If you’re an SLP who works with patients with Parkinson’s, chances are you’ve encountered variable speech outcomes in those who have been treated with STN-DBS (subthalamic nucleus deep brain stimulation). While the STN-DBS treatment may be beneficial for the patient’s motor symptoms, there can be unwelcome side effects on speech intelligibility. As the authors of the study I read point out, patients are sometimes unaware of the possibility of speech becoming worse after this treatment. From a clinician’s perspective, it would be ideal to have a good idea of what subset of patients are likely to have minimal vs major negative effects on their speech. Together with information from their neurologist and surgeon, this would help SLPs in counseling patients considering this big step.
To identify predictors of speech outcomes status post STN-DBS, the authors gathered a sample of fifty-four consecutive patients. All patients underwent STN-DBS, with two neurosurgeons blinded to the results of speech data independently determining anatomic location of each electrode contact (in the axial and coronal planes, relative to the subthalamic nucleus). Each patient was administered a speech assessment (described below) in two conditions – on-medication and off-medication) at two time points – prior to surgery and one year post-surgery.
The speech assessment consisted of the following: the Assessment of Intelligibility for Dysarthric Speech (AIDS) and a 60-second monologue. A single native-English speaking speech and language therapist (SLT – this study took place in the UK) rated the sentences from the AIDS per the Darley, Aronson, and Brown scale. Since multiple speech characteristics were rated, the SLT first completed the overall intelligibility rating to attempt to control for effects of familiarity in subsequent replays of the speech samples. Then, each speech characteristic cluster in the DAB scale was rated. These included: respiration, articulation, phonation, resonance, prosody, and rate. Sound pressure level (dB SPL) was measured via clinical software, and rate in words per minute was calculated (total number of words/total minutes of speech sample) per the AIDS manual.
Outcomes data consisted of change in speech intelligibility from baseline to 1-year in two conditions: on- and off-medication. Loudness and scores on the subscales of the DAB scale were secondary outcomes. The main findings of the study were:
- Overall deterioration in speech intelligibility after one year of DBS by 14.4% (off-medication condition) and 12.7% (on-medication)
- On-medication condition one year post DBS: more significant decline in articulation, followed by prosody, phonation, respiration, rate, and resonance, in that order
- Off-medication condition one year post DBS: more significant decline in articulation, followed by respiration, rate of speech, and resonance; no significant decline in prosody or phonation in off-medication condition (at least, as measured by DAB scale by a single rater)
- Factors predictive of speech outcomes: preoperative speech performance, disease duration, UPDRS-III off-medication score
- Factors not predictive of speech outcomes: age
- Medially placed left brain electrodes (left in relation to the STN, between the red nucleus and the STN) affects speech negatively, especially in patients who have had Parkinson’s for a long time
The neurosurgeons and neuroscientists authoring this study rightly focus on the issue of electrode placement for much of the article’s discussion. As a speech-language pathologist, I do think that’s helpful information to be able to make better sense of the surgery notes when doing a chart review (if available). Simply knowing that the left active electrode has been placed medially to the STN gives me a heads-up that this client may not make as much progress as similar patients with more ideal electrode placement. I would incorporate this fact into my clinical documentation to explain progress and, depending on the patient’s speech severity, help justify the need for any alternative & augmentative avenues taken in therapy.
The other results are helpful for counseling patients who have concerns with their speech, either pre-DBS or post-DBS. For instance, I’ve worked with a couple patients whose neurologists considered them a candidate for DBS, but the patients were on the fence about proceeding. Based on this article, I can provide accurate information that yes, their speech is likely to decline after DBS, and they will need to weigh that risk against the benefit of motor improvements. In collaboration with their neurologist, I could also counsel them that, if they are considering DBS, the effect on their speech at least is likely to be better if they proceed with DBS sooner rather than later in the disease course. (In any such discussion, the intent is simply to provide the information for the patient to make an informed decision.)
Please see the reference below if you’d like to read the article for yourself.
Tripoliti, E., Zrinzo, L., Martinez-Torres, I., Frost, E., Pinto, S., Foltynie, T., … Limousin, P. (2011). Effects of subthalamic stimulation on speech of consecutive patients with Parkinson disease. Neurology, 76(1), 80–86. doi:10.1212/WNL.0b013e318203e7d0
For more information on Research Tuesday, please visit Gray Matter Therapy. Happy researching!