Supplementary Motor Area Syndrome: Characteristics, Symptoms And Causes

The supplementary motor area is a region located in the frontal lobe of the brain, responsible for functions such as the initiation, preparation and coordination of motor actions, as well as other processes related to language.

When a part of this brain area is removed or injured, supplementary motor area syndrome may occur In this article we explain what it is and what the main characteristics of supplementary motor area syndrome and the brain region that is affected by it are. We also tell you about the clinical signs and symptoms it causes, and how to make a differential diagnosis of this disorder.

The supplementary motor area: characteristics, location and functions

To understand what supplementary motor area syndrome consists of, we must first delve into the characteristics and main functions of a region of the brain as important as the supplementary motor area.

This brain region is located in the medial aspect of the frontal lobe It extends posteriorly to the primary motor cortex and inferiorly to the cingulate gyrus. It belongs to Brodmann’s area 6 and is part of the motor cortex, and more specifically, the secondary motor cortex (along with the premotor area).

Researchers have divided the supplementary motor area, at least, into two different parts: the presupplementary motor area, which would be responsible for initiating movements in response to external and environmental stimuli; and the supplementary motor area itself, whose functions include managing the initiation of internally generated voluntary motor sequences.

The supplementary motor area is, as we mentioned, a key region for initiating motor actions, but also plays an important role in the motivation necessary for movement to occur This also occurs with the processes involved in speech, since the activation of this area is also essential to initiate acts of verbal communication.

On the other hand, activation of the supplementary motor area occurs when carrying out complex motor sequences that require fine and precise movements (e.g. hand sewing or drawing). Furthermore, in various studies it has been found that this area is also activated when we imagine that we are performing a specific movement, even if it is not put into practice later.

In studies carried out with subjects who have suffered injuries to this brain area, it has been proven that, when damage occurs in the left supplementary motor area, transcortical motor aphasia usually occurs, which It is characterized by a deficit in language comprehension, both verbal and written although, on the other hand, the patient maintains a certain verbal fluency.

Another disorder related to damage to this region of the brain that we will talk about throughout the article is supplementary motor area syndrome. Let’s see what it consists of.

What is supplementary motor area syndrome?

Supplementary motor area syndrome is a disorder that results from surgical resection or injury of the brain region that bears its name It was Laplane, who in 1977 described the clinical evolution of supplementary motor area syndrome in patients who had undergone such resection surgery.

This researcher observed that lesions in the supplementary motor area produced a characteristic syndrome that evolves in three stages:

1. After surgery and resection of the supplementary motor area

The patient, immediately after surgery and resection of the supplementary motor area, experiences global akinesia (more pronounced on the contralateral side) and language arrest

2. A few days after recovery

The patient, a few days after recovery after surgery, experiences a severe reduction of spontaneous motor activity on the contralateral side, facial paralysis and reduction of spontaneous speech

3. Time after surgery

Time after resective surgery occurs, the patient will have long-term consequences which include the alteration of fine and precise hand movements, such as alternating movements, especially in complex tasks.

Characteristics and main symptoms

The main characteristic of supplementary motor area syndrome is its transitory nature and its complete reversibility, which can occur within a period that is generally less than 6 months The patient recovers automatic movements before voluntary ones, something logical if one takes into account that the management of internally generated movements predominates in the supplementary motor area (without external stimulation), with respect to motor actions initiated from external stimuli.

The patient’s recovery is based on neuronal plasticity mechanisms that facilitate the transfer of information from the supplementary motor area to its contralateral counterpart. With everything, The patient will experience clinical signs and symptoms that will last as long as it takes for recovery to be complete

The syndrome of the supplementary motor area generates seizures, which cause tonic postures that include flexion of the contralateral elbow, abduction of the arm with external rotation of the shoulder, as well as head and eye deviation. These epileptic seizures usually last a few seconds (between 5 and 30) and are characterized by being quite frequent, without auras, with a sudden start and end, in addition to predominating during the patient’s sleep and when vocalizing.

Transcortical motor aphasia occurs in practically all cases in which the lesion occurs in the dominant hemisphere and in several studies, it has been highlighted that the majority of patients also present severe hemiparesis with motor neglect.

Language disorders in people affected by supplementary motor area syndrome have the following characteristics:

Differential diagnosis

The differential diagnosis of patients with supplementary motor area syndrome (SAMS) It is usually performed with people who have motor deficits in the immediate postoperative period and lesions of the corticospinal tract which is characterized by an increase in muscle stretch reflexes, unlike what occurs in SAMS.

In some cases, the motor deficit could be considered motor neglect, rather than hemiparesis , since many times verbal stimuli elicit a motor response from the affected hemibody. Recovery from SAMS includes the participation of the uninjured hemisphere, in which the SAMS takes a predominant role to begin the relearning of movements.