SMA Syndrome stands for Supplementary Motor Area Syndrome. It is a temporary neurosurgical condition first documented in 1977 and arises from damage to the supplementary motor area of the brain. It occurs in 26-100% of surgeries that take place in one of the two supplementary motor areas.
We can think of it in 3 phases, which we’ll break down here in our Key Clinical Features and Prognosis sections:
- Akinetic mutism
- Difficulty speaking and/or moving one side of the body
But first – what is the SMA?
The supplementary motor area (SMA) , also known as Brodmann Area 6c, is an eloquent area of the brain – ‘eloquent’ means it performs ‘higher level’ functions. It is found in the posterior third of the superior frontal gyrus in the frontal lobe of the brain, and contains 90% of all corticospinal neurons – which run from the cerebral cortex to the spinal cord. Its job is to coordinate movement and speech.
Each SMA controls movement on the opposite (contralateral) side of the body from where it sits – our left SMA controls the right side of our bodies and vice versa. This process was first discovered by American neurosurgeon Wilder Penfield and his team in 1951, when they used electrical stimulation on the brain’s surface and observed loss of speech and motion in the opposite side of the patient’s body.
What Causes SMA Syndrome?
The exact cause is unknown, but currently attributed to damage to the SMA, either during surgery for frontal lobe epilepsy or for tumour removal. In the latter case, we often see SMA syndrome more frequently with lower grade tumours – most frequently WHO-grade II gliomas – as opposed to high grade tumours. Other causes have been suggested too, such as impact of retraction during surgery, or postoperative swelling (oedema).
What are the Key Clinical Features of SMA Syndome?
The majority of the symptoms of SMA syndrome are transient. Features can be correspond to the phases we mentioned earlier.
SMA Syndrome – Phase 1: Akinesia –loss of movement – is often apparent in early stages of this condition, affecting the the opposite side of the body to the location of surgery (AKA hemiparalysis). Typically, the patient will still retain their muscle strength. Additionally, mutism – loss of speech – can be associated with akinesia in these cases and, along with other speech deficits, more frequently occurs in cases where the dominant SMA has been involved in the operation.
SMA Syndrome – Phase 2: includes less severe speech deficits and contralateral motor weakness known as hemiparesis. Other motor deficits can also manifest, such as apraxia (loss of movement coordination) and dyspraxia (partial loss of movement coordination). Facial paresis (weakness) is also sometimes noted in SMA syndrome at this stage too.
What is the Prognosis for SMA Syndrome?
SMA Syndrome – Phase 3: remission/recovery. SMA syndrome tends to resolve on its own, without medication or further surgery; the exact process of resolution is unknown, but it may be due to the other, unaffected SMA becoming more active to compensate for the deficits that we see here. This process is known as plasticity and it has been attributed to the strong connections between each SMA in the brain.
We normally have an improvement within the first week of the operation, with longer recovery times are associated with surgeries taking place in deeper areas of the SMA.
On average it can take up to 8 months for speech deficits to fully recover and usually about 3 months for motor deficits. It is quite normal to also see some mild, permanent, motor deficits. Usually these are to do with alternating, one-sided movements and do not generally affect quality of life.
- SMA syndrome is a common complication of neurosurgery in the SMA
- It affects speech and movement
- Symptoms of SMA syndrome are usually temporary and resolve on their own soon after surgery.
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Brainbook Editorial Officer
At the time of writing, Ameerah is a third-year student studying Neuroscience at the University of Glasgow.