In this post, we are going to be talking about Mirror movement disorder (MMD) using a case study. Sometime in the recent past, I was going through my message requests, and something caught my attention: a clearly exasperated mother was laying a complaint about some bizarre movements she had noticed in her son. One hand seemed not to have a will of its own; it seemed to be enslaved to the will of the other hand and simultaneously copied exactly whatever the other hand did.
She had gone to several hospitals, seen different doctors, including paediatric neurologists, but none seemed to understand the bizarre pattern of movements her toddler son was exhibiting.
There were a series of videos of the boy engaged in different activities sent with the complaints that were meant to help me understand what the mother was describing. When I clicked on them to watch, my eyes almost popped out of their sockets. Right there, I could see, for the first time myself, an interesting pattern of movements so rare that the incidence is about 1 in a million population, and most people, even some doctors, are unaware of.
Imagine that you are standing in front of a mirror with your side turned to it, in such a way that only one side of your body is seen in the mirror. Any movement you make, say with your hand, your reflection in the mirror would do the same, at the same time, only in the reverse direction, wouldn’t it?
Exactly what it was like!
In one of the videos, while the 2 year old is holding a spoon with his right hand, trying to scoop a spoonful of rice, there is a mirror reversal of the same movement on the left hand: it is clenched as if holding a spoon, and at the same time making scooping movements in the opposite direction. In another video, while the child is trying to unscrew the cover of a can of bottled water, the other hand is busy mimicking the same movement, so much the child has to grip the can with his thighs for support as the free hand can’t be used to grip it for support.
Classical case of what is called Mirror Movement Disorder.
DECLARATION OF CONSENT
Just in case you were wondering, inasmuch as no information that could be used to identify the patient or his mother was disclosed, express consent was sought and obtained from the mother before writing this.
Also, the purpose of this write up, which is mainly to create awareness, as well as the media through which it may be disseminated, was disclosed to her, and her approval was obtained.
In her own words.“Please go on [and write on it]. I thought of telling you to write about it, but I felt that would be asking for too much. It took me almost two years to get an answer [on what is actually wrong with my son]. Reading the comments on that YouTube video you sent me, I found out it took some people decades! Besides, I am in academia, and I care about sound knowledge, especially when it concerns health. Thank you for taking it up….”
Disorders of the nervous system are usually difficult to explain, and even more difficult to understand, even for some doctors.
What is Mirror movement disorder?
MMD is a disorder of coordination, usually classified as a “Developmental Coordination Disorder,” in which voluntary/intentional movement on a part, usually the hands and fingers, of one side of the body, is accompanied by an involuntary/unintentional mirroring of the same movement on the other side of the body.
Other terms used to describe it include Bimanual Synkinesis, Hand Mirror Movements, Mirror Hand Movements, etc.
Understanding Mirror Movement Disorder; Mechanism of Mirror movement disorder
The human brain consists of two hemispheres, the right, and the left hemispheres. These hemispheres usually control and coordinate movement on the opposite side of the body; so, while the right hemisphere is in charge of the left side of the body, the left hemisphere is the orchestra commandant for the right side.
Both hemispheres are connected in the middle by a structure called the corpus callosum, through which they constantly exchange information. However, despite this connection, and the fact that both hemispheres are usually “aware” of each other’s activities, the wiring of the brain is in such a way that there are inhibitions that prevent one hemisphere from acting out the other’s actions.
This arrangement ensures a sort of “functional independence” that allows for the possibility of simultaneous mutually exclusive movements in both sides of the body. Thus one can perform different movements at the same time, and with two opposing limbs, in such a well-coordinated fashion as to enhance dexterity: a boxer, for instance, can throw a punch with one hand, and defend at the same time with the other hand. Likewise, a driver can be steering his car with one hand and be controlling the gear lever at the same time with the other hand. Similarly, one can stabilize a can of bottled water with the non-dominant hand, while unscrewing the cover with the dominant hand, and would not find it difficult.
In mirror movement disorder, however, the brain is rewired in such a way that, not just are the two hemisphere aware of each other’s actions, the inhibitions that keep them from acting it out is removed, functional independence is therefore lost, and the limbs end up enslaved to each other’s will: while one is carrying out a voluntary movement, the other involuntarily joins it in sympathy by performing a synkinetic mirror reversal of the same movements.
To understand why this happens, and how it happens, one need to be acquainted with a broader phenomenon- the phenomenon of SYNKINESIS.
Synkinesis
The prefix ‘syn-‘ means “acting/considered together.” The suffix ‘-kinesis,’ on the other hand means ‘movement.’ So synkinesis literally means synchronous movement, or movement occurring at the same time.
Medically speaking, synkinesis is defined as a neurological symptom in which a voluntary muscle movement causes the simultaneous involuntary contraction of other muscles.
The prerequisite for synkinesis is a neurological injury- that is an injury to nerves, followed by an abnormal rewiring when the damaged nerve tries to grow back.
Each nerve is like a wire wrapped up in an insulating material called myelin sheath, which shields it from electrical impulses from surrounding nerves, and is then carefully guided to the particular structure [muscle or gland] it supplies and provides motor function to. This arrangement ensures that when a nerve is stimulated, only the muscle it supplies moves, of all the muscles in that same neighbourhood. Thus, one can blink an eye, without wrinkling his nose, or smiling, and vice versa.
Following a nerve injury, however, the insulation provided by the myelin sheath may be lost, allowing for abnormal interactions, called “crosstalks,” between nerves. Also, while the nerve is growing back, its branches may make abnormal connections, not just with the muscle it previously supplied, but also with others in the same neighbourhood as the muscle. While the former phenomenon is called ephaptic transmission, the latter is called aberrant nerve regeneration. Both can lead to synkinesis, either while acting in concert, or individually.
Examples of synkinesis.
1. Sometimes after Bell’s palsy, in which the facial nerve is damaged, one can develop Bogorad’s syndrome, otherwise called the “crocodile tears syndrome.” In this, part of the injured and healing facial nerve, that is responsible for salivation, makes an abnormal connection with the tear gland on the same side of the face. Thus, whenever the person salivates- for instance on seeing, or perceiving the smell of, food; tears start flowing from the eyes.
2. In another type of facial nerve injury, a smile, or twitching of one corner of the mouth, is usually accompanied by involuntary blinking, or closure of the eye of the same side.
Mirror movement disorder as a form of bimanual/bilateral synkinesis
MMD is a form of synkinesis. The only difference between it and other forms of synkinesis is the fact that it happens on muscle groups that are not in the same neighbourhood, and are in fact far apart, and on opposite sides of the body. Thus, it is a form of synkinesis referred to as bimanual, or bilateral synkinesis.
Unlike in other forms of synkinesis where the precipitating neurological damage, and subsequent rewiring, happens in a peripheral nerve, in mirror movement disorder it occurs in the brain. Also, while the basic pathophysiologic mechanism is the same, that of mirror movement disorder is a little bit more complex.
In the growing brain, the brain hemispheres do not just control the opposite sides of the body, as earlier stated. This is because in new-borns, the pyramidal tract, the principle nerve pathway through which the brain bring about movement in the limbs, doesn’t just project from a brain hemisphere to the opposite side of the body, as it does in adults; instead, it projects from each hemisphere to both sides of the body. Also, the nerve fibres in the corpus callosum, the structure that connects both sides of the brain, are not insulated from each other, and therefore have free “crosstalks” between themselves.
Due to these reasons, the two sides of the brain are not functionally independent in new-borns: they, more or less, function as a single unit. Thus, both hands usually do the same thing in babies: moro reflex, for instance, sees both arms abduct and adduct at the same time; and a child invariably grabs the breasts with two hands, and similarly instinctively reaches for an object, say a toy, when offered, with both hands. As a matter of fact, arm preference, or selective handedness, in a child below a certain age, raises concerns as it usually suggests an abnormality, such as paralysis, or cerebral palsy, affecting predominantly the less used side.
This natural phenomenon, of a child’s both hands mirroring each other during bimanual activities, is called Physiological Mirror Movements.
As a child grows, however, brain development and maturation also continues progressively. With this, more and more nerves in the corpus callosum become insulated[myelinated], limiting crosstalks. Also, the nerves in the pyramidal tract become myelinated, as are the inhibitory nerves in the cerebral cortex. These selectively inhibit projections from each hemisphere to the same side, ensuring that each hemisphere only controls the opposite side, as is the case in adults.
With increasing age, more and more tendencies for instances of “mirror movements” are lost. By 7 to 10 years, when the corpus callosum, and the pyramidal tract, are fully insulated/myelinated, mirror movements would no longer be possible, except in the following circumstances.
1. In people who are genetically predisposed to having abnormal brain wiring.
2. In children with a brain insult or injury that may halt the normal development process, and may therefore interfere with myelination, for instance in some cases of cerebral palsy.
3. Brain injury or insult in a fully developed brain that may lead to “rewiring” during healing, or loss of cortical inhibition due to the injury itself. Examples include stroke, and Parkinson’s disease.
Types of mirror movement disorder [MMD]
MMDs are broadly classified into 2 types.
1. Congenital MMD
2. Acquired MMD
Congenital mirror movement disorder
Congenital MMD are usually present from birth, hence the term “congenital.” They are caused by genetic mutations in genes that regulate the growth and development of certain nerve cells in the brain, and particularly dictate the patterns of migration of the axons of brain nerve cells across the midline. These genes include the DCC and RAD51 genes. Mutations in them usually run in families and can be inherited in an autosomal recessive, or autosomal dominant pattern.
They account for the majority of cases of mirror movement disorder (MMD) in the population, usually persist throughout the person’s life, and neither gets better, nor worse with age.
Mirror movement disorder can also be seen in certain congenital syndromes, and diseases, for example Kallman’s Syndrome, Klippel-Feil Syndrome, and Congenital Hemiplegia, a form of Cerebral Palsy in which the inciting injury, which is usually periventricular leukomalacia, happens inside the womb.
Acquired mirror movement disorder
Acquired MMD is a term used for MMDs that are neither congenital, nor inherited, but are instead caused by either a direct brain injury or insult, or other diseases that affect the brain in one way or the other.
They can start manifesting in childhood or adulthood, depending on when the inciting injury or event occurred.
Known causes include the following.
- Cerebral Palsy
- Epilepsy
- Stroke
- Parkinson’s Disease
- ALS
- Phenylketonuria
- Friedreich’s Ataxia
- Alien Hand Syndrome
- Obsessive-Compulsive Disorder
- Schizophrenia
Influence on quality of life
The major influence on the quality of life is due to its limitation of dexterity. This, depending on the severity, and may affect various range of activities, extending from simple to complex ones. This may have far reaching effects on one’s education [as writing may be difficult], occupation, and sometimes even simple activities of daily living.
It could also affect one’s psychological health mainly due to the distress and worries it may cause, as well as the fallouts of bullying and social stigmatization.
It is usually a purely motor phenomenon, and DOESN’T AFFECT COGNITION and INTELLECT, except if the inciting injury or condition caused considerable damage to other parts of the brain.
How is MMD diagnosed?
Recognizing mirror movements is usually pretty straightforward. While mirrored movements are involuntary, and occur intermittently as they parallel voluntary movements, they are not paroxysmal. This helps distinguish them from other involuntary hand movements such as choreo-athetoid movements, and seizures.
While recognizing mirror movements may be relatively straightforward, one must remember that they are merely a symptom complex, and not a diagnosis in themselves. Effort should therefore be made to figure out if it is isolated or accompanied by other features that may suggest it being part of a syndrome, or manifestation of an established neurological disease.
Age, as well as onset of symptoms, is important to rule out physiological mirror movements, as well as to differentiate congenital from acquired forms of mirror movement disorder.
Genetic tests, as well as neuroimaging, and relevant ancillary tests, are important in making a definitive diagnosis.
Management of Mirror movement disorder
Mirror Movement Disorders are poorly understood. That coupled with the fact that it involves the brain, a part of the body populated by permanent cells, makes treatment largely supportive than curative.
As already stated, Congenital MMDs are permanent, and persist throughout life. Measures such as occupational therapy, to help the patient learn to live and cope better with the disorder, as well as appropriate psychological interventions, may be quite helpful.
For the acquired causes, in addition to the above stated, specific treatments directed at the cause, or inciting medical condition, may prove helpful.
PROGNOSIS
Prognosis depends on the type.
The congenital, or genetic types, for instance, last for a lifetime. The outcome of the acquired types, on the other hand, depend on the cause, and severity of injury.
Physiological variants, that is the ones that are part of normal development, usually resolve by 7 to 10 years.
The aim of this series was to draw attention to, and create awareness about, mirror movements– a one-in-a-million neurological disorder, that can either exist on its own, or along with other medical conditions.
I hope I have done that successfully.
My special appreciation goes to the mother whose son’s case prompted this series, for giving her consent for me to write about this. As well as to you all who were patient enough to indulge me throughout the course of this series.
Gracias!
REFERENCES
Congenital Movement Disorder [ April, 2020]. In Wikipedia. Retrieved from: https://en.m.wikipedia.org/wiki/Congenital_mirror_movement_disorder?fbclid=IwAR1UI5U0AUJI6iX_a6q4WnBAQeGs26Mb-BsdJIrAUvPcdYN4BOrSQV-TRPA
Galléa, C., Popa, T., Billot, S. et al. Congenital mirror movements: a clue to understanding bimanual motor control. J Neurol 258, 1911–1919 (2011). https://doi.org/10.1007/s00415-011-6107-9
He JL, Fuelscher I, Enticott PG, Teo WP, Barhoun P, Hyde C. Interhemispheric Cortical Inhibition Is Reduced in Young Adults With Developmental Coordination Disorder. Front Neurol. 2018;9:179. Published 2018 Mar 23. doi:10.3389/fneur.2018.00179.
Nadkarni NA, Deshmukh SS. Mirror movements.Ann Indian Acad Neurol. 2012;15(1):13‐14. doi:10.4103/0972-2327.93268.
Synkinesis [April, 2020]. In Wikipedia. Retrieved from: https://en.wikipedia.org/wiki/Synkinesis