Facial Synkinesis is a common sequela to Idiopathic Facial Nerve Paralysis, also called Bell’s Palsy or Facial Palsy. Bell’s Palsy, which is thought to occur due to a viral reactivation which can lead (through unknown mechanisms) to diffuse axon demyelination and degeneration of the seventh cranial nerve, results in a hemifacial paralysis due to non-functionality of the nerve. As the nerve attempts to recover, nerve miswiring results (see Mechanism of Action below). In patients with severe facial nerve paralysis, facial synkinesis will inevitably develop.

Additionally, a common treatment option for facial palsy is to use electrical stimulation. Unfortunately, this has been shown to be disruptive to normal re-innervation and can promote the development of synkinesis.

The most common symptoms of facial synkinesis include:

- Eye closure with volitional contraction of mouth muscles

- Midfacial movements with volitional eye closure

- Neck tightness (Platysmal contraction) with volitional smiling

- Hyperlacrimation(also called Crocodile Tears)

- A case where eating provokes excessive lacrimation. This has been attributed to neural interaction between the salivary glands and the lacrimal glands.

Synkinesis is the result from miswiring of nerves after trauma. This result is manifested through involuntary muscular movements accompanying voluntary movements. For example, voluntary smiling will induce an involuntary contraction of the eye muscles causing the eye to squint when smiling. Most commonly involved are facial muscles and the extraocular muscles, rarely the hands are performing mirror movements.

Causes are diverse and include nerve trauma with improper healing, or nerve degeneration, as in the course of Parkinson´s disease. In congenital cases, mutations of genes involved in nerve growth, specifically axonal growth have been found. Rarely, it is part of syndromes with neuroendocrine problems such as Kallman syndrome.

The prognosis is usually good with normal intelligence and lifespan. Treatment depends on the cause, but is largely conservative with facial retraining or mime therapy, if needed, while Botox and surgery are used as last resort.

Marcus Gunn phenomenon, also known as Marcus Gunn jaw-winking or trigemino-oculomotor synkinesis, is an autosomal dominant condition with incomplete penetrance, in which nursing infants will have rhythmic upward jerking of their upper eyelid. This condition is characterized as a synkinesis: when two or more muscles that are independently innervated have either simultaneous or coordinated movements.

Common physiologic examples of synkineses occur during sucking, chewing, or conjugate eye movements. There are also several abnormal cranial nerve synkineses, both acquired and congenital. Marcus Gunn jaw-winking is an example of a pathologic congenital synkinesis.

First described by the ophthalmologist Marcus Gunn in 1883, this condition presents in approximately 5% of neonates with congenital ptosis. This condition has been associated with amblyopia (in 54% of cases), anisometropia (26%), and strabismus (56%).

It has been postulated that the synkinesis is due to damage to cranial nerve nuclei, caused by peripheral nerve injury and the nuclear lesion releases evolutionarily older [neural] mechanisms with their tendency toward associated movements, and so primitive reflexes are not inhibited.

Marcus Gunn jaw-winking is an exaggeration of a very weak physiologic co-contraction that has been disinhibited secondary to a congenital brain stem lesion. The stimulation of the trigeminal nerve by contraction of the pterygoid muscles of jaw results in the excitation of the branch of the oculomotor nerve that innervates the levator palpebrae superioris ipsilaterally (on the same side of the face), so the patient will have rhythmic upward jerking of their upper eyelid.

There are two major groups of trigemino-oculomotor synkineses:

1) External pterygoid-levator synkinesis is when the eyelid raises upon:

- Jaw thrust to opposite side (homolateral external pterygoid)

- Jaw is projected forward (bilateral external pterygoid)

- Mouth is opened widely

2) Internal pterygoid-levator synkinesis is when the eyelid raises upon teeth clenching

External pterygoid-levator synkinesis is the more common group.

Bell's palsy is a type of facial paralysis that results in an inability to control the facial muscles on the affected side. Symptoms can vary from mild to severe. They may include muscle twitching, weakness, or total loss of the ability to move one or rarely both sides of the face. Other symptoms include drooping of the eyelid, a change in taste, pain around the ear, and increased sensitivity to sound. Typically symptoms come on over 48 hours.

The cause of Bell's palsy is unknown. Risk factors include diabetes and a recent upper respiratory tract infection. It results from a dysfunction of cranial nerve VII (the facial nerve). Many believe that this is due to a viral infection that results in swelling. Diagnosis is based on a person's appearance and ruling out other possible causes. Other conditions that can cause facial weakness include brain tumor, stroke, Ramsay Hunt syndrome, and Lyme disease.

The condition normally gets better by itself with most achieving normal or near-normal function. Corticosteroids have been found to improve outcomes, while antiviral medications may be of a small additional benefit. The eye should be protected from drying up with the use of eye drops or an eyepatch. Surgery is generally not recommended. Often signs of improvement begin within 14 days, with complete recovery within six months. A few may not recover completely or have a recurrence of symptoms.

Bell's palsy is the most common cause of one sided facial nerve paralysis (70%). It occurs in 1 to 4 per 10,000 people per year. About 1.5% of people are affected at some point in their life. It most commonly occurs in people between ages 15 and 60. Males and females are affected equally. It is named after Scottish surgeon Charles Bell (1774–1842), who first described the connection of the facial nerve to the condition.

Bell's palsy is characterized by a one-sided facial droop that comes on within 72 hours. In rare cases (<1%), it can occur on both sides resulting in total facial paralysis.

The facial nerve controls a number of functions, such as blinking and closing the eyes, smiling, frowning, lacrimation, salivation, flaring nostrils and raising eyebrows. It also carries taste sensations from the anterior two-thirds of the tongue, via the chorda tympani nerve (a branch of the facial nerve). Because of this, people with Bell's palsy may present with loss of taste sensation in the anterior 2/3 of the tongue on the affected side.

Although the facial nerve innervates the stapedial muscles of the middle ear (via the tympanic branch), sound sensitivity and dysacusis are hardly ever clinically evident.

Although defined as a mononeuritis (involving only one nerve), people diagnosed with Bell’s palsy may have "myriad neurological symptoms" including "facial tingling, moderate or severe headache/neck pain, memory problems, balance problems, ipsilateral limb paresthesias, ipsilateral limb weakness, and a sense of clumsiness" that are "unexplained by facial nerve dysfunction".

Damage to the corpus callosum can give rise to "purposeful" actions in the sufferer's non-dominant hand (an individual who is left-hemisphere-dominant will experience the left hand becoming alien, and the right hand will turn alien in the person with right-hemisphere dominance).

In "the callosal variant", the patient's hand counteracts voluntary actions performed by the other, "good" hand. Two phenomena that are often found in patients with callosal alien hand are "agonistic dyspraxia" and "diagonistic dyspraxia".

Agonistic dyspraxia involves compulsive automatic execution of motor commands by one hand when the patient is asked to perform movements with the other hand. For example, when a patient with callosal damage was instructed to pull a chair forward, the affected hand would decisively and impulsively push the chair backwards.

Agonistic dyspraxia can thus be viewed as an involuntary competitive interaction between the two hands directed toward completion of a desired act in which the affected hand competes with the unaffected hand to complete a purposive act originally intended to be performed by the unaffected hand.

Diagonistic dyspraxia, on the other hand, involves a conflict between the desired act in which the unaffected hand has been engaged and the interfering action of the affected hand which works to oppose the purpose of the desired act intended to be performed by the unaffected hand. For instance, when Akelaitis's patients underwent surgery to the corpus callosum to reduce epileptic seizures, one patient's left alien hand would frequently interfere with the right hand. For instance, while trying to turn over to the next page with the right hand, his left hand would try to close the book.

In another case of callosal alien hand, the patient did not suffer from intermanual conflict between the hands but rather from a symptom characterized by involuntary mirror movements of the affected hand. When the patient was asked to perform movements with one hand, the other hand would involuntarily perform a mirror image movement which continued even when the involuntary movement was brought to the attention of the patient, and the patient was asked to restrain the mirrored movement. The patient suffered from a ruptured aneurysm near the anterior cerebral artery, which resulted in the right hand being mirrored by the left hand. The patient described the left hand as frequently interfering and taking over anything the patient tried to do with the right hand. For instance, when trying to grasp a glass of water with the right hand with a right side approach, the left hand would involuntary reach out and grasp hold of the glass through a left side approach.

More recently, Geschwind et al. described the case of a woman who suffered severe coronary heart disease. One week after undergoing coronary artery bypass grafting, she noticed that her left hand started to "live a life of its own". It would unbutton her gown, try to choke her while asleep and would automatically fight with the right hand to answer the phone. She had to physically restrain the affected hand with the right hand to prevent injury, a behavior which has been termed "self-restriction". The left hand also showed signs of severe ideomotor apraxia. It was able to mimic actions but only with the help of mirror movements executed by the right hand (enabling synkinesis). Using magnetic resonance imaging (MRI), Geschwind et al. found damage to the posterior half of the callosal body, sparing the anterior half and the splenium extending slightly into the white matter underlying the right cingulate cortex.

Alien hand syndrome (AHS) is a condition in which a person experiences their limbs acting seemingly on their own, without control over the actions. The term is used for a variety of clinical conditions and most commonly affects the left hand. There are many similar names used to describe the various forms of the condition but they are often used inappropriately. The afflicted person may sometimes reach for objects and manipulate them without wanting to do so, even to the point of having to use the controllable hand to restrain the alien hand. While under normal circumstances, thought, as intent, and action can be assumed to be deeply mutually entangled, the occurrence of alien hand syndrome can be usefully conceptualized as a phenomenon reflecting a functional "disentanglement" between thought and action.

Alien hand syndrome is best documented in cases where a person has had the two hemispheres of their brain surgically separated, a procedure sometimes used to relieve the symptoms of extreme cases of epilepsy and epileptic psychosis, e.g., temporal lobe epilepsy. It also occurs in some cases after brain surgery, stroke, infection, tumor, aneurysm, migraine and specific degenerative brain conditions such as Alzheimer's disease and Creutzfeldt–Jakob disease. Other areas of the brain that are associated with alien hand syndrome are the frontal, occipital, and parietal lobes.

Disfigurement is the state of having one's appearance deeply and persistently harmed medically, such as from a disease, birth defect, or wound. General societal attitudes towards disfigurement have varied greatly across cultures and over time, with cultures possessing strong social stigma against it often causing psychological distress to disfigured individuals. Alternatively, many societies have regarded some forms of disfigurement in a medical, scientific context where someone having ill will against the disfigured is viewed as anathema. In various religious and spiritual contexts, disfigurement has been vaoriously described as being as a punishment from the divine for sin (such as Yahweh's defacement of Cain for Abel's murder in Judaism), as being (such as Paul of the New Testament's arguments about Christ's sufferings) caused by supernatural forces of hate and evil against the good and just, which will be later atoned for, or as being without explanation "per se" with people just having to endure.

The topic has been frequently commented on and referred to in a great many forms of fictional media as well. Villainous examples include the iconic fiend The Joker from various DC Comics and the mysterious figure with a "red right hand" from the song of the same name by band Nick Cave and the Bad Seeds. Heroic examples include Daredevil, a crime-fighter who was rendered blind (from Marvel Comics), and the compassionate character Edward Scissorhands from the film of the same name.

Conditions that can cause disfigurement include:

- severe acne

- acromegaly

- amniotic band constriction

- amputation

- argyria

- birthmarks

- burns

- cancer

- cataracts

- circumcision

- cleft lip

- eczema

- elephantiasis

- erysipelas

- gangrene

- gigantomastia

- gynecomastia

- keloids

- leprosy

- necrosis

- McCune–Albright syndrome

- neurofibromatosis

- noma

- paralysis

- proteus syndrome

- radiation poisoning

- scalping

- scars

- smallpox

- severe strabismus

- synkinesis

- Syphilis

- vitiligo

- severe warts

Plastic surgery or reconstructive surgery is available in many cases to disfigured people. Some health insurance companies and government health care systems cover plastic surgery for these problems when they do not generally cover plastic surgery for what is labeled as "cosmetic purposes".

The term "disfigurement" is sometimes used pejoratively to describe the results of intentional body modification. Scarification and other forms of such modification will sometimes be referred to as such by neutral parties or by advocates of the processes as well. Many types of body modification are subject to strong social debate as such.

Congenital hypogonadotropic hypogonadism presents as hypogonadism, e.g., reduced or absent puberty, low libido, infertility, etc. due to an impaired release of the gonadotropins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and a resultant lack of sex steroid and peptides production by the gonads.

In Kallmann syndrome, a variable non-reproductive phenotype occurs with anosmia (loss of the sense of smell) including sensorineural deafness, coloboma, bimanual synkinesis, craniofacial abnormalities, and/or renal agenesis.

Isolated hypogonadotropic hypogonadism (IHH), also called idiopathic or congenital hypogonadotropic hypogonadism (CHH), as well as isolated or congenital gonadotropin-releasing hormone deficiency (IGD), is a condition which results in a small subset of cases of hypogonadotropic hypogonadism (HH) due to deficiency in or insensitivity to gonadotropin-releasing hormone (GnRH) where the function and anatomy of the anterior pituitary is otherwise normal and secondary causes of HH are not present.