""Astasia" redirects here. This term was also applied to chlorophyll-less "Euglena.

Astasis is a lack of motor coordination marked by an inability to stand, walk or even sit without assistance due to disruption of muscle coordination.

The term "astasia" is interchangeable with "astasis" and is most commonly referred to as "astasia" in the literature describing it. Astasis is the inability to stand or sit up without assistance in the absence of motor weakness or sensory loss (although the inclusion of 'the lack of motor weakness' has been debated by some physicians). It is categorized more as a symptom than an actual disease, as it describes a disruption of muscle coordination resulting in this deficit. The disturbance differs from cerebellar ataxia in that with astasis the gait can be relatively normal, with balance significantly impaired during transition from a seated to standing position. This balance impairment is similar to patients with vestibulocerebellar syndrome, which is a progressive neurological disease with many symptoms and effects.

Astasis has been seen in patients with diverse thalamic lesions, predominantly affecting the posterior lateral region of the brain. It is most frequently accompanied by abasia, although not always. Abasia is a symptom very similar to it and is the inability to walk. The two are most commonly seen in astasia-abasia, which is also called Blocq's disease. It is more common for astasia and abasia to be seen together than it is to see either one or the other.

There are many speculations as to what is the main cause of astasis. A combination of weakness of the triceps surae muscle, peripheral neuropathy, and irregular postural movements are the leading theories thus far. Diabetes, spinal root or spinal cord lesions, and traumas or injuries to the motor cortex of the brain can also cause similar symptoms that are seen in patients with astasis. However, none of these have been proven definite. Many scientists also believe that this is a conversion disorder, in which patients exhibit symptoms without any neurological cause.

Recent population-based studies have estimated the prevalence of NPH to be about 0.5% in those over 65 years old, with an incidence of about 5.5 patients per 100,000 of people per year. This is in accordance with comparable findings stating that although normal pressure hydrocephalus can occur in both men and women of any age, it is found more often in the elderly population, with a peak onset generally in the sixth to seventh decades.

Abasia (from Greek: "a-", without and "basis", step) is the inability to walk owing to impairment in motor coordination.

The term covers a spectrum of medical disorders such as:

- choreic abasia: caused by chorea of the legs

- paralytic abasia: caused by paralysis of the leg muscles

- spastic abasia: caused by spastic stiffening of the leg muscles

- trembling abasia: caused by trembling of the legs

Abasia is frequently accompanied by astasis, an inability to stand, see Astasia-abasia.

Astasia-abasia refers to the inability to either stand or walk in a normal manner. Astasia refers to the inability to stand upright unassisted. Abasia refers to lack of motor coordination in walking. The term "abasia" literally means that the base of gait (the lateral distance between the two feet) is inconstant or unmeasurable. When seen in conversion disorder, the gait is bizarre and is not suggestive of a specific organic lesion: often the patient sways wildly and nearly falls, recovering at the last moment.

An acquired total inability to stand and walk can be seen in true neurological diseases, including stroke, Parkinson's disease, damage to the cerebellum, Guillain–Barré syndrome, normal pressure hydrocephalus and many others. In normal pressure hydrocephalus, for example, when the condition remains untreated, the patient's gait becomes shortened, with frequent shuffling and falls; eventually standing, sitting, and even rolling over in bed become impossible. This advanced state is referred to as "hydrocephalic astasia-abasia".

Astasia and/or abasia are associated with the corresponding fears of walking and/or standing, variously called stasophobia, basophobia, stasiphobia, basiphobia, stasobasophobia, stasibasiphobia, etc., sometimes turning into pathological forms, i.e. phobias.

Patients with dementia who are confined to a nursing home and may have undiagnosed NPH can possibly become independent again once treated. So far only one study was able to evaluate the prevalence of NPH, both diagnosed and undiagnosed, among residents of assisted-living facilities, showing a prevalence in 9 to 14% of the residents.

NPH may be relieved by surgically implanting a ventriculoperitoneal shunt to drain excess cerebrospinal fluid to the abdomen where it is absorbed. Once the shunt is in place, the ventricles usually diminish in size in 3 to 4 days, regardless of the duration of the hydrocephalus. Even though the ventricular swelling diminishes, only 21% of patients show a marked improvement in symptoms. The most likely patients to show improvement are those that show only gait disturbance, mild or no incontinence, and mild dementia. A more recent study (2004) found better outcomes, concluding that if patients with idiopathic normal pressure hydrocephalus are correctly identified, shunt insertion yielded beneficial outcomes in 86% of patients, in either gait disturbance (81%), improved continence (70%), or both. They also observed that measurements in the diagnostic clinical triad, the cortical sulci size, and periventricular lucencies were related to outcome. However, other factors such as age of the patient, symptom duration, dilation of ventricles, and the degree of presurgical dementia were unrelated to outcome.

Brain related causes are less commonly associated with isolated vertigo and nystagmus but can still produce signs and symptoms, which mimic peripheral causes. Disequilibrium is often a prominent feature.

- Degenerative: age related decline in balance function

- Infectious: meningitis, encephalitis, epidural abscess, syphilis

- Circulatory: cerebral or cerebellar ischemia or hypoperfusion, stroke, lateral medullary syndrome (Wallenberg's syndrome)

- Autoimmune: Cogan syndrome

- Structural: Arnold-Chiari malformation, hydrocephalus

- Systemic: multiple sclerosis, Parkinson's disease

- Vitamin deficiency: Vitamin B12 deficiency

- CNS or posterior neoplasms, benign or malignant

- Neurological: Vertiginous epilepsy, abasia

- Other – There are a host of other causes of dizziness not related to the ear.

- Mal de debarquement is rare disorder of imbalance caused by being on board a ship. Patients suffering from this condition experience disequilibrium even when they get off the ship. Typically treatments for seasickness are ineffective for this syndrome.

- Motion sickness – a conflict between the input from the various systems involved in balance causes an unpleasant sensation. For this reason, looking out of the window of a moving car is much more pleasant than looking inside the vehicle.

- Migraine-associated vertigo

- Toxins, drugs, medications; it is also a known symptom of carbon monoxide poisoning.

Causes of dizziness related to the ear are often characterized by vertigo (spinning) and nausea. Nystagmus (flickering of the eye, related to the Vestibulo-ocular reflex [VOR]) is often seen in patients with an acute peripheral cause of dizziness.

- Benign Paroxysmal Positional Vertigo (BPPV) – The most common cause of vertigo. It is typically described as a brief, intense sensation of spinning that occurs when there are changes in the position of the head with respect to gravity. An individual may experience BPPV when rolling over to the left or right, upon getting out of bed in the morning, or when looking up for an object on a high shelf. The cause of BPPV is the presence of normal but misplaced calcium crystals called otoconia, which are normally found in the utricle and saccule (the otolith organs) and are used to sense movement. If they fall from the utricle and become loose in the semicircular canals, they can distort the sense of movement and cause a mismatch between actual head movement and the information sent to the brain by the inner ear, causing a spinning sensation.

- Labyrinthitis - An inner ear infection or inflammation causing both dizziness (vertigo) and hearing loss.

- Vestibular neuronitis - an infection of the vestibular nerve, generally viral, causing vertigo

- Cochlear Neuronitis – an infection of the Cochlear nerve, generally viral, causing sudden deafness but no vertigo

- Trauma – Injury to the skull may cause either a fracture or a concussion to the organ of balance. In either case an acute head injury will often result in dizziness and a sudden loss of vestibular function.

- Surgical trauma to the lateral semicircular canal (LSC) is a rare complication which does not always result in cochlear damage. Vestibular symptoms are pronounced. Dizziness and instability usually persist for several months and sometimes for a year or more.

- Ménière's disease - an inner ear fluid balance disorder that causes lasting episodes of vertigo, fluctuating hearing loss, tinnitus (a ringing or roaring in the ears), and the sensation of fullness in the ear. The cause of Ménière's disease is unknown.

- Perilymph fistula – a leakage of inner ear fluid from the inner ear. It can occur after head injury, surgery, physical exertion or without a known cause.

- Superior canal dehiscence syndrome – a balance and hearing disorder caused by a gap in the temporal bone, leading to the dysfunction of the superior canal.

- Bilateral vestibulopathy – a condition involving loss of inner ear balance function in both ears. This may be caused by certain antibiotics, anti-cancer, and other drugs or by chemicals such as solvents, heavy metals, etc., which are ototoxic; or by diseases such as syphilis or autoimmune disease; or other causes. In addition, the function of the semicircular canal can be temporarily affected by a number of medications or combinations of medications.

Many different causes of aboulia have been suggested. While there is some debate about the validity of aboulia as a separate disease, experts mostly agree that aboulia is the result of frontal lesions and not with cerebellar or brainstem lesions. As a result of more and more evidence showing that the mesolimbic and the mesocortical dopamine system are key to motivation and responsiveness to reward, aboulia may be a dopamine-related dysfunction. Aboulia may also result from a variety of brain injuries which cause personality change, such as dementing illnesses, trauma, or intracerebral hemorrhage (stroke), especially stroke causing diffuse injury to the right hemisphere.

A lack of motivation has been reported in 25–50% of patients with Alzheimer's disease. While depression is also common in patients with this disease, aboulia is not a mere symptom of depressions because more than half of the patients with Alzheimer's disease with aboulia do not suffer from depression. Several studies have shown that aboulia is most prevalent in cases of severe dementia which may result from reduced metabolic activity in the prefrontal regions of the brain. Patients with Alzheimer's disease and aboulia are significantly older than patients with Alzheimer's who do not lack motivation. Going along with that, the prevalence of aboulia increased from 14% in patients with a mild case Alzheimer's disease to 61% in patients with a severe case of Alzheimer's disease, which most likely developed over time as the patient got older.

Empirical studies have found that the prognosis for conversion disorder varies widely, with some cases resolving in weeks, and others enduring for years or decades. There is also evidence that there is no cure for Conversion Disorder, and that although patients may go into remission, they can relapse at any point. Furthermore, many patients who are 'cured' continue to have some degree of symptoms indefinitely.

Information on the frequency of conversion disorder in the West is limited, in part due to the complexities of the diagnostic process. In neurology clinics, the reported prevalence of unexplained symptoms among new patients is very high (between 30 and 60%). However, diagnosis of conversion typically requires an additional psychiatric evaluation, and since few patients will see a psychiatrist it is unclear what proportion of the unexplained symptoms are actually due to conversion. Large scale psychiatric registers in the US and Iceland found incidence rates of 22 and 11 newly diagnosed cases per 100,000 person-years, respectively. Some estimates claim that in the general population, between 0.011% and 0.5% of the population have conversion disorder.

For a long time, the fear of falling was merely believed to be a result of the psychological trauma of a fall, also called "post-fall syndrome". This syndrome was first mentioned in 1982 by Murphy and Isaacs, who noticed that after a fall, ambulatory persons developed intense fear and walking disorders. Fear of falling has been identified as one of the key symptoms of this syndrome. Since that time, FOF has gained recognition as a specific health problem among older adults. However, FOF was also commonly found among elderly persons who had not yet experienced a fall.

Prevalence of FOF appears to increase with age and to be higher in women. Age remains significant in multiple logistic regression analyses. The results of different studies have reported gender as a somewhat significant risk factor for fear of falling. Other risk factors of fear of falling in the elderly include dizziness, self-rated health status, depression, and problems with gait and balance.

The fear of falling (FOF), also referred to as basophobia (or basiphobia), is a natural fear and is typical of most humans and mammals, in varying degrees of extremity. It differs from acrophobia (the fear of heights), although the two fears are closely related. The fear of falling encompasses the anxieties accompanying the sensation and the possibly dangerous effects of falling, as opposed to the heights themselves. Those who have little fear of falling may be said to have a head for heights. Basophobia is sometimes associated with astasia-abasia, the fear of walking/standing erect.