It is common practice to assume that cerebral stroke causes muscular weakness in swallowing and that strength based exercises help fix it. This makes no sense from a theoretical physiological perspective or from what is often seen on fluoro. Here’s why (a thread) #FOAMed

Cerebral stroke causes limb weakness because the voluntary movement of the limbs is controlled by contralateral motor pathways from the motor cortex through the descending pyramidal tracts to the spinal cord and relevant limb. Infarction thus stops the message from being sent.

Most of the cranial nerves however are (mostly) bilaterally innervated (with the exception of XII and VII*) *sort of, this is a thread in itself. I.e in a PACS stroke you may have a tongue deviation but you’ll never see a unilateral jaw dislocation. This is half the story...

Swallowing, breathing and coughing aren’t voluntary movements like lifting an arm, at least not exclusively. Many animal studies have shown that decerebration (chopping off the brain above brainstem) results in loss of voluntary movement but cough, swallow and breathing go on.

How so? Recall that the centres that hold the blue print for swallowing are housed in the medulla and so as long as the medulla is intact, swallowing, coughing and breathing continue.

So why do stroke patients have dysphagia? Well because as many studies have shown, without cortical inputs the swallow response in the brain stem is a crude swallow not tailored to the volume or texture of the bolus. It is a mere airway protection reflex like cough.

Consistent with the lived experience of eating and drinking we choose when to swallow, and we realise that we need to swallow harder and longer for steak than for water. Also we have to swallow faster for water than for mashed potato.

So the deficits in swallowing are that one does not swallow hard enough, fast enough, or long enough for the relevant bolus resulting in pre swallow aspiration or post swallow residue (a slight over-simplification but also basically what’s happening)

A lot of the sensory information to calibrate the swallow is gained from the oral stage and a hemisensory disturbance distorts this (recall that unlike bulbar innervation which is bilateral, sensation is contralateral)

Consider how your speech sounds after a trip to the dentist after an alveolar nerve block. Your muscles haven’t been anaesthetised, your sensation is off. You rely on sensation to put your lips and tongue in the right place (keep this in mind for #dysarthria treatment)

Although you may have lip and tongue weakness for voluntary movement after stroke, reflex action (swallowing) is preserved, this is true even in bilateral stroke (see locked in syndrome or FCMS)

So if dysphagia is mostly caused by sensori-motor incoordination, does strength based exercise make sense?(spoilers, no) however do not despair. Because skill training is on hand to save the day.

Skill training teaches people to manually override their swallow speed, strength and duration and there are a variety of biofeedback tools that can help people relearn what to do (VF, FEES, sEMG)

And of course, the age old practice of starting with something you can swallow easily (e.g purée) and gradually making it more difficult (thinner or more bulky) is excellent rehab

but we shouldn’t wait for spontaneous recovery, find the level where they are struggling and practice! (E.g. That was good but try and swallow it quicker and harder/try and make the waveform bigger/try and make the whiteout last longer

And of course these deficits coexist with problems with oral containment, chewing, self feeding ability and cognitive impairment so individualised treatment programmes are needed.

#dysphagia and swallowing are magnificent and complex and elegant, and if you thought swallowing was just about the cranial nerves (paging Mr Henry Marsh) then think again