Typical and Atypical DBS Side Effects

Deep brain stimulation provides benefit when applied properly and the benefit should persist for decades. Configuring stimulation parameters to optimize benefit while avoiding side effects is paramount to prolonged success and patient satisfaction. Optimal stimulation requires precisely positioned electrodes into a specific location in the brain that is about the size of a pea. Therefore, surgical skill in electrode placement is the first step in success over the lifetime.

Applying adequate stimulation through an excellent positioned electrode is associated with lasting benefit and has less risk of causing symptoms to worsen right after surgery. However, stimulation induced side effects will occur if  stimulation is not adjusted properly. Using a less than excellent electrode may lessen side effects but may also lead to less benefit and require more battery power to reach the beneficial areas. Skilled programming adjustments are the second link in success and happiness with DBS. Even well placed electrodes can be rendered ineffective if not programmed properly.

Typical and Reversible Stimulation Side Effects

Well positioned electrodes can cause reversible stimulation induced side effects that can include any of the following signs or symptoms: tingling, numbness, poor coordination, muscle tightness, muscle twitching or contraction, sense of heaviness, speech change, swallowing change, worse walking and balance, vision change, dizziness, nausea, hot flash, anxiety, depression, mania, impulsivity, mental fog, verbal fluency decline, minor shocks or electrical surges, pulsations, coarse tremoring and pain.

The good news is  stimulation side effects are reversible by adjusting stimulation settings while maintaining benefit. Side effects do not lead to symptom improvement and therefore should be avoided.

Atypical Reversible and Irreversible Stimulation Side Effects

Poor or inadequate surgical planning or electrode placement can cause poor results and unintended persistent problems after surgery. New or worsening problems with walking, balance, muscle tightness, coordination, speech, mood and cognition can occur and may not be reversible. Applying stimulation using poorly positioned electrodes may cause or worsen these disabling symptoms.

The timeline of events is essential when investigating new or worsening problems after DBS surgery. Patients generally know when their body changed for the worse. If the change happened prior to activating stimulation, the surgical plan and awake intraoperative testing can be analyzed to discover any irregularities that may have led to worsening symptoms. If the change happened after adjusting stimulation, then the stimulation parameters may need further consideration. After the brain has healed from surgery, any decline in symptoms should be investigated and stimulation adjusted if indicated to eliminate side effects.

Bottom line

Stimulation should always work in the right patient with adequate electrode placement and proper stimulation settings. The skills and knowledge of the surgeon and programmer will set the bar for the success of DBS over the lifetime.

 

Speech Quality & DBS

Speech & DBS

Speech Spectrogram
Speech Spectrogram – Computerized Voice Assessment

Speech changes are a common symptom of Parkinson’s, tremor or dystonia. The cause is multifactorial and typically speech changes occur very slowly over time. (This distinction is important.) Speech can also be altered by deep brain stimulation and is one of the most common stimulation related side effects and great source of patient dissatisfaction. Almost all speech disturbances can be reversed if the speech change is related to stimulation.

Other causes of speech problems after DBS can occur from the surgery such as bleeding (stoke) or tissue damage. These complications are uncommon but are serious and may involve more than just speech, such as walking and thinking. Having a stoke from other causes (high cholesterol, high blood pressure) can also cause speech problems and are unrelated to DBS.

Speech changes can also occur from too low or too high medication dose, dyskinesia, tremor, fatigue and illness. The vocal cords can be a source of voice change but is typically noticed prior to DBS and should always be assessed by an ENT physician specialist. A change in speech can be a sign of a serious medical conditions.

Stimulation dose is not much different than medication dose. Too little dose – not enough benefit, too high dose – side effects occur. Stimulation and medication are similar in that there is a maximum benefit and always a risk of side effect if the dose is too high.

Useful Tips: The following are some tips that patients can use to assist their medical provider in troubleshooting speech problems after DBS.

Before DBS:

  1. See a speech therapist for a computerized speech assessment – on medications. This is the benchmark for all future speech assessments after DBS.
  2. Optimize speech, posture and breathing for the best possible speech before surgery.
  3. Optimal speech depends on optimal medication if you have Parkinson’s.
  4. Make a recording of your speech to use later if needed to assess speech changes.

After DBS:

  1. Write down for you doctor when your speech was the best and when you first noticed a change. Some patients remember one appointment that resulted in speech slurring. I see some patients that tell me speech was good a couple years ago and then started to get worse. This could be disease progression or it could be from a gradual increase in stimulation intensity. The time-line will help determine what caused speech to change. Note how your speech changed, such as loss of volume, mumbling, stuttering or slurring. If you have a recording of your speech when it was good, bring it to your appointment.

How I assess speech changes in my patients after DBS:

  1. If the speech change occurs prior to turning on stimulation for the first time, I assess and monitor cognition. If the speech change is related to a change in verbal fluency (cognition), it may improve over a few months. Verbal fluency problems are related to finding the right word or completing sentences (language aspect of cognition) but commonly lumped into the speech category after DBS.
  2. If the speech change is after stimulation has been on, I set up an appointment to specifically assess speech. The patient should be On medications for the appointment. I use a simple assessment to establish a baseline by asking my patients to read the rainbow passage. I audio-record speech if the problem is complicated. I then turn off one side at a time. If speech improves with stimulation off, I adjust stimulation parameters to eliminate the speech problems. This is generally not difficult if the speech problem is from overstimulation.
  3. Almost always, the cause of the speech problem is too high stimulation intensity. This is a very reversible cause and reducing stimulation intensity can resolve almost all speech problems related to DBS. This assumes good placement of the electrodes in the brain. During DBS surgery, I talk with my patients to ensure speech is not being impacted to optimize electrode placement. (One very good reason to have DBS while awake)
  4. A common myth is that only the left side of the brain is involved in causing speech problems. This is not true. The left brain does control language for many people, but then so does the right brain in some. Language and speech are two very different functions controlled by very different areas of the brain.
  5. Tremor is one of the most common causes of pushing stimulation too high. I think this is most likely because we can see the tremor and tremor will increase with emotions and stress. Some patients and medical providers expect tremor to just stop instantly and if it doesn’t, stimulation intensity is increased until tremor stops, even when stimulation causes the leg to drag, the hand to cramp, speech to slur or balance problems. However, like with other symptoms, it takes time for stimulation to work. Over-stimulating will stop tremor quickly but will more than likely cause un-necessary speech problems and most importantly can also cause swallowing problems, falls and increased slowness and stiffness (like the tin-man). Having appropriate expectations for DBS and knowing the limits can help avoid stimulation side effects and symptoms that mimic disease progression.