The first major form relates to an abnormality of the brain called an Arnold–Chiari malformation or Chiari Malformation. This is the most common cause of syringomyelia, where the anatomic abnormality, which may be due to a small posterior fossa, causes the lower part of the cerebellum to protrude from its normal location in the back of the head into the cervical or neck portion of the spinal canal. A syrinx may then develop in the cervical region of the spinal cord. Here, symptoms usually begin between the ages of 25 and 40 and may worsen with straining, called a valsalva maneuver, or any activity that causes cerebrospinal fluid pressure to fluctuate suddenly. Some patients, however, may have long periods of stability. Some patients with this form of the disorder also have hydrocephalus, in which cerebrospinal fluid accumulates in the skull, or a condition called arachnoiditis, in which a covering of the spinal cord—the arachnoid membrane—is inflamed.

Some cases of syringomyelia are familial, although this is rare.

Generally, there are two forms of syringomyelia: congenital and acquired. (In addition, one form of the disorder involves the brainstem. The brainstem controls many of our vital functions, such as respiration and heartbeat. When syrinxes affect the brainstem, the condition is called syringobulbia.)

Arachnoiditis is a chronic disorder with no known cure, and prognosis may be hard to determine because of an unclear correlation between the beginning of the disease and the appearance of symptoms. For many, arachnoiditis is a disabling disease that causes chronic pain and neurological deficits, and may also lead to other spinal cord conditions, such as syringomyelia.

The root cause of the condition is not entirely clear, and it appears to have multiple causes, including iatrogenic cause from misplaced epidural steroid injection therapy when accidentally administered intrathecally (inside the dura mater, the sac enveloping the arachnoid mater), or from contrast media used in myelography prior to the introduction of Metrizamide. Other noninfectious inflammatory processes include surgery, intrathecal hemorrhage, and the administration of anesthetics (e.g. chloroprocaine), and steroids (e.g. prednisolone, triamcinolone acetonide). A variety of other causes exist, including infectious, inflammatory, and neoplastic processes. Infectious causes include bacterial, viral, fungal, and parasitic agents. Prior spinal surgery has been documented as a cause of "arachnoiditis ossificans", as well as for the adhesive form. It can also be caused by long term pressure from either a severe disc herniation or spinal stenosis.

Diastematomyelia (occasionally diastomyelia) is a congenital disorder in which a part of the spinal cord is split, usually at the level of the upper lumbar vertebra.

Diastematomyelia is a rare congenital anomaly that results in the "splitting" of the spinal cord in a longitudinal (sagittal) direction. Females are affected much more commonly than males. This condition occurs in the presence of an osseous (bone), cartilaginous or fibrous septum in the central portion of the spinal canal which then produces a complete or incomplete sagittal division of the spinal cord into two hemicords. When the split does not reunite distally to the spur, the condition is referred to as a diplomyelia, or true duplication of the spinal cord.

Scoliosis affects 2–3% of the United States population, which is equivalent to about 5 to 9 million cases. A scoliosis spinal column's curve of 10° or less affects 1.5% to 3% of individuals. The age of onset is usually between 10 years and 15 years (can occur at a younger age) in children and adolescents, making up to 85% of those diagnosed. This is seen to be due to rapid growth spurts occurring at puberty when spinal development is most relenting to genetic and environmental influences. Because female adolescents undergo growth spurts before postural musculoskeletal maturity, scoliosis is more prevalent among females. Although fewer cases are present today using Cobb angle analysis for diagnosis, scoliosis remains a prevailing condition, appearing in otherwise healthy children. Incidence of idiopathic scoliosis (IS) stops after puberty when skeletal maturity is reached, however, further curvature may proceed during late adulthood due to vertebral osteoporosis and weakened musculature.

Kyphoscoliosis may manifest in an individual at different stages of life and for various causes. When present at a young age ranging from childhood to teenage, Kyphoscoliosis may be present from birth due to congenital abnormalities including Spina bifida.

In a few cases, it may also be the result of keeping an abnormal posture or slouching for a prolonged period which causes an abnormal curvature of the spine.

Certain infections can also lead to the development of Kyphoscoliosis such as vertebral tuberculosis or general tuberculosis. Osteochondrodysplasia, a disorder related to the development of bone and cartilage, can also cause this disease.

In later ages, Kyphoscoliosis can occur in patients suffering from chronic degenerative diseases like osteoporosis and Osteoarthritis. This type of incidence is usually seen in patients above 50+ years of age and is mainly attributed to structural changes in the spine and adjoining tissues. Sometimes, a traumatic injury can also lead to its development.

Further, there are many idiopathic occurrences of Kyphoscoliosis where the exact cause is not very well known but is suspected to be caused by genetic factors.

The prevalence of congenital Chiari I malformation, defined as tonsilar herniations of 3 to 5 mm or greater, was previously believed to be in the range of one per 1000 births, but is likely much higher. Women are three times more likely than men to have a congenital Chiari malformation. Type II malformations are more prevalent in people of Celtic descent. A study using upright MRI found cerebellar tonsillar ectopia in 23% of adults with headache from motor-vehicle-accident head trauma. Upright MRI was more than twice as sensitive as standard MRI, likely because gravity affects cerebellar position.

Cases of congenital Chiari malformation may be explained by evolutionary and genetic factors. Typically, an infant's brain weighs around 400g at birth and triples to 1100-1400g by age 11. At the same time the cranium triples in volume from 500 cm to 1500 cm to accommodate the growing brain. During human evolution, the skull underwent numerous changes to accommodate the growing brain. The evolutionary changes included increased size and shape of the skull, decreased basal angle and basicranial length. These modifications resulted in significant reduction of the size of the posterior fossa in modern humans. In normal adults, the posterior fossa comprises 27% of the total intracranial space, while in adults with Chiari Type I, it is only 21%. If a modern brain is paired with a less modern skull, the posterior fossa may be too small, so that the only place where the cerebellum can expand is the foramen magnum, leading to development of Chiari Type I. H. neanderthalensis had platycephalic (flattened) skull. Some cases of Chiari are associated with platybasia (flattening of the skull base).

The most widely accepted pathophysiological mechanism by which Chiari type I malformations occur is by a reduction or lack of development of the posterior fossa as a result of congenital or acquired disorders. Congenital causes include hydrocephalus, craniosynostosis (especially of the lambdoid suture), hyperostosis (such as craniometaphyseal dysplasia, osteopetrosis, erythroid hyperplasia), X-linked vitamin D-resistant rickets, and neurofibromatosis type I. Acquired disorders include space occupying lesions due to one of several potential causes ranging from brain tumors to hematomas.

Head trauma may cause cerebellar tonsillar ectopia, possibly because of dural strain. Additionally, ectopia may be present but asymptomatic until whiplash causes it to become symptomatic. Posterior fossa hypoplasia causes reduced cerebral and spinal compliance.

The cost of scoliosis involves both monetary losses and lifestyle limitations that increase with severity. Respiratory deficiencies may also arise from thoracic deformities and cause abnormal breathing. This directly affects exercise and work capacity, decreasing the overall quality of life.

In the health care system of the United States, the average hospital cost for cases involving surgical procedures was $30,000 to $60,000 per patient in 2010. As of 2006, the cost of bracing has been published as up to $5,000 during rapid growth periods, when braces must be consistently replaced across multiple follow-ups.

Surgery

Surgical intervention is warranted in patients who present with new onset neurological signs and symptoms or have a history of progressive neurological manifestations which can be related to this abnormality. The surgical procedure required for the effective treatment of diastematomyelia includes decompression (surgery) of neural elements and removal of bony spur. This may be accomplished with or without resection and repair of the duplicated dural sacs. Resection and repair of the duplicated dural sacs is preferred since the dural abnormality may partly contribute to the "tethering" process responsible for the symptoms of this condition.

Post-myelographic CT scanning provides individualized detailed maps that enable surgical treatment of cervical diastematomyelia, first performed in 1983.

Observation

Asymptomatic patients do not require surgical treatment. These patients should have regular neurological examinations since it is known that the condition can deteriorate. If any progression is identified, then a resection should be performed.

Syringobulbia is a medical condition in which syrinxes, or fluid-filled cavities, affect the brainstem. This defect normally results from congenital abnormality, trauma or tumor growth.

It mostly occurs within the lower brainstem as a slit-like gap. This may affect one or more cranial nerves, resulting in various kinds of facial palsies. Sensory and motor nerve pathways may be affected by interruption or compression of nerves. This disorder is associated with syringomyelia, a syrinx limited to the spinal cord.

Chiari-like malformation (CM) is the most common cause of foramen magnum obstruction and syringomyelia in dogs. Syringomyelia (SM) is a disease of the spinal cord typified by fluid filled cavities, or syrinxes, within the spinal cord substance. The disease is caused by the obstruction of cerebrospinal fluid (CSF), in the nervous system. A situation of high pressure in the spinal cord compared to low pressure outside, leads to fluid accumulation, which eventually forms cavities. CM is a condition characterized by the mismatch of size between the brain and the skull. The skull is too small causing part of the brain to descend out of the skull through the opening at its base, crowding the spinal cord. The cause of CM is not yet fully understood. CM is rare in most breeds but reportedly has become very widespread in the Cavalier King Charles Spaniel and the Griffon Bruxellois (Brussels Griffon). As many as 95% of Cavalier King Charles Spaniels may have CM. It is worldwide in scope and not limited to any country, breeding line, or kennel, and experts report that it is believed to be inherited in the Cavalier King Charles Spaniel. CM is so widespread in the Cavalier that it may be an inherent part of the CKCS's breed standard. This disease not only affects thousands of dogs, but a similar condition affects over three hundred thousand children yearly. Therefore, canines are an appropriate model for the treatment of the human condition.

Basilar invagination can be present at birth. If the condition develops after birth, it is usually the result of injury or diseases. If due to injury, about half the time it is caused by vehicle or bicycle accidents; 25% of the time by falls and 10% of the time by recreational activities such as diving accidents.

It also occurs in patients with bone diseases, such as osteomalacia, rheumatoid arthritis, Paget's disease, Ehlers-Danlos syndrome, Marfan syndrome, and osteogenesis imperfecta.

A study measured outcome from surgery of 49 cases of scoliosis and kyphoscoliosis. Of this sample, 36 patients were monitored for a period of 8 years.

- 23% - excellent condition

- 29% - good condition

- 34% - satisfactory

- 14% - bad

Bad refers to cases where the surgery failed to address the disease and the patient either had to undergo a revision surgery or continues to suffer from a poor quality of life as before surgery.

It should be noted that typically post-surgery complications range up to 5% involving all major and minor complications when measured within one year of surgery. However, there may be a progressive decline in patient’s condition after a few years.

In another study that evaluated surgical treatment of kyphoscoliosis and scoliosis due to congenital reasons, 91% of surgeries were found to be successful and met their intended objectives for the two-year follow-up period after surgery. The sample consisted of 23 patients of whom 17 were male and 6 were female, with an average age of 27 years, ranging from 13 to 61 years. The most popular type of surgeries for spinal correction includes pedicle subtraction osteotomy (PSO) and posterior vertebral column resection (pVCR).

Another study which focused on elderly patients found that the rate of complications was much higher for a sample population of 72 cases with mean age of 60.7 years. The rate of complications was as high as 22% in the entire sample. The study points that in the case of elderly patients, surgery should only be considered when there is no other option left; the disease is in progression stage, and the quality of life has degraded to an extent where conservative treatments can no longer help with pain.

While there are many surgical approaches for spinal deformity correction including anterior only, posterior only, anterior-posterior, the techniques that are most popular nowadays include the posterior only VCR or pVCR. One of the studies which analyze pVCR technique also noted the benefit of using a technique called NMEP monitoring in assisting the surgeon avoid any neurological complications while performing a spine surgery.

In conclusion, the decision to undergo a corrective spine surgery is a complex one but sometimes becomes necessary when the quality of life has degraded to such an extent that potential benefits outweigh the risks. No surgery is devoid of risks but by carefully assessing factors such as the skills and experience of the surgical team, previous record or history of outcomes, and the techniques that are used for spine surgery, a patient along with his or her doctor can certainly help in achieving a successful outcome.

As studies are repeatedly pointing out, the success rates for spinal surgeries have improved so much so that the risks rates can now be comparable to other types of surgeries. These success rates also tend to be higher at a younger age when compared to the elderly age.

Basilar invagination is invagination (infolding) of the base of the skull that occurs when the top of the C2 vertebra migrates upward. It can cause narrowing of the foramen magnum (the opening in the skull where the spinal cord passes through to the brain). It also may press on the lower brainstem.

This is similar to Chiari malformation. That, however, is usually present at birth.

The type of treatment needed for dogs diagnosed with CM/SM depends on the severity of the condition and the age of the dog. Young dogs with clinical signs should be considered for surgical removal to minimize the progression of the disease as the dog ages. Older dogs with little or no clinical signs may be treated medically, rather than surgically. However, severe cases of CM/SM may require surgery regardless of age. The goal of surgery is syrynx decompression through restoration of normal cerebrospinal fluid circulation.

The surgical treatment of CM in dogs is described as "foramen magnum decompression FMD". Despite an approximately 80% success rate with this surgical technique, there is a 25% to 50% relapse, primarily due to excessive scar tissue formation at the decompression site. A cranioplasty may be performed instead, in which a plate, constructed using titanium mesh and bone cement, is fixed to the back of the skull following a standard FMD procedure. The procedure had been effective in humans. The postoperative relapse rate associated with the titanium cranioplasty procedure is less than 7%.

Dissociated sensory loss is a pattern of neurological damage caused by a lesion to a single tract in the spinal cord which involves "selective" loss of fine touch and proprioception "without" loss of pain and temperature, or vice versa.

Understanding the mechanisms behind these selective lesions requires a brief discussion of the anatomy involved.

Loss of pain and temperature are due to damage to the lateral spinothalamic tracts, which cross the central part of the cord close to the level where they enter it and travel up the spinal column on the opposite side to the one they innervate (i.e. they "ascend contralaterally"). Note that a lesion of the lateral spinothalamic tract at a given level will not result in sensory loss for the dermatome of the same level; this is due to the fibers of the tract of Lissauer which transmit the neuron one or two levels above the affected segment (thus bypassing the segmental lesion on the contralateral side).

Loss of fine touch and proprioception are due to damage to the dorsal columns, which do not cross the cord until the brainstem, and so travel up the column on the same side to the one they innervate (i.e. they "ascend ipsilaterally").

This means that a lesion of the dorsal columns will cause loss of touch and proprioception below the lesion and on the same side as it, while a lesion of the spinothalamic tracts will cause loss of pain and temperature below the lesion and on the opposite side to it.

Dissociated sensory loss always suggests a focal lesion within the spinal cord or brainstem.

The location of cord lesions affects presentation—for instance, a central lesion (such as that of syringomyelia) will knock out second order neurons of the spinothalamic tract as they cross the centre of the cord, and will cause loss of pain and temperature without loss of fine touch or proprioception.

Other causes of dissociated sensory loss include:

- Diabetes mellitus

- Syringomyelia

- Brown-Séquard syndrome

- Lateral medullary syndrome aka Wallenberg's syndrome

- Anterior spinal artery thrombosis

- Tangier disease

- Subacute combined degeneration

- Multiple sclerosis

- Tabes dorsalis

- Friedreich's ataxia (or other spinocerebellar degeneration)

Subglottic stenosis is a congenital or acquired narrowing of the subglottic airway. Although it is relatively rare, it is the third most common congenital airway problem (after laryngomalacia and vocal cord paralysis). Subglottic stenosis can present as a life-threatening airway emergency. It is imperative that the otolaryngologist be an expert at dealing with the diagnosis and management of this disorder. Subglottic stenosis can affect both children and adults.

Subglottic stenosis can be of three forms, namely congenital subglottic stenosis, idiopathic subglottic stenosis (ISS) and acquired subglottic stenosis. As the name suggests, congenital subglottic stenosis is a birth defect. Idiopathic subglottic stenosis is a narrowing of the airway due to an unknown cause. Acquired subglottic stenosis generally follows as an after-effect of airway intubation, and in extremely rare cases as a result of gastroesophageal reflux disease (GERD).

Subglottic stenosis is graded according to the Cotton-Meyer classification system from one to four based on the severity of the blockage.

Grade 1 – <50% obstruction

Grade 2 – 51–70% obstruction

Grade 3 – 71–99% obstruction

Grade 4 – no detectable lumen

Treatments to alleviate the symptoms of subglottic stenosis includes a daily dose of steroids such as prednisone, which reduces the inflammation of the area for better breathing. Other medications such as Methotrexate is also being tested by patients but results are pending.

Other causes may include:

- Anticonvulsant pharmaceutical drugs, such as topiramate, sultiame, and acetazolamide

- Anxiety and/or panic disorder

- Benzodiazepine withdrawal syndrome

- Beta alanine

- Carpal tunnel syndrome

- Cerebral amyloid angiopathy

- Chiari malformation

- Coeliac disease (celiac disease)

- Complex regional pain syndrome

- Decompression sickness

- Dehydration

- Dextromethorphan (recreational use)

- Fabry disease

- Erythromelalgia

- Fibromyalgia

- Fluoroquinolone toxicity

- Guillain–Barré syndrome (GBS)

- Heavy metals

- Herpes zoster

- Hydroxy alpha sanshool, a component of Sichuan peppers

- Hyperglycemia (high blood sugar)

- Hyperkalemia

- Hyperventilation

- Hypoglycemia (low blood sugar)

- Hypocalcemia, and in turn:

- Hypermagnesemia, a condition in which hypocalcemia itself is typically observed as a secondary symptom

- Hypomagnesemia, often as a result of long term proton-pump inhibitor use

- Hypothyroidism

- Immunodeficiency, such as chronic inflammatory demyelinating polyneuropathy (CIDP)

- Intravenous administering of strong pharmaceutical drugs acting on the central nervous system (CNS), mainly opioids, opiates, narcotics; especially in non-medical use (drug abuse)

- Ketorolac

- Lidocaine poisoning

- Lomotil

- Lupus erythematosus

- Lyme disease

- Menopause

- Mercury poisoning

- Migraines

- Multiple sclerosis

- Nitrous oxide, long-term exposure

- Obdormition

- Pyrethrum and pyrethroid (pesticide)

- Rabies

- Radiation poisoning

- Sarcoidosis

- Scorpion stings

- Spinal disc herniation or injury

- Spinal stenosis

- Stinging nettles

- Syringomyelia

- Transverse myelitis

- Vitamin B deficiency

- Vitamin B deficiency

- Withdrawal from certain selective serotonin reuptake inhibitors (or serotonin-specific reuptake inhibitors) (SSRIs), such as paroxetine or serotonin-norepinephrine reuptake inhibitors (SNRIs) such as venlafaxine

The importance of correctly recognizing progressive muscular atrophy as opposed to ALS is important for several reasons.

- 1) the prognosis is a little better. A recent study found the 5-year survival rate in PMA to be 33% (vs 20% in ALS) and the 10-year survival rate to be 12% (vs 6% in ALS).

- 2) Patients with PMA do not suffer from the cognitive change identified in certain groups of patients with MND.

- 3) Because PMA patients do not have UMN signs, they usually do not meet the "World Federation of Neurology El Escorial Research Criteria" for “Definite” or “Probable” ALS and so are ineligible to participate in the majority of clinical research trials such as drugs trials or brain scans.

- 4) Because of its rarity (even compared to ALS) and confusion about the condition, some insurance policies or local healthcare policies may not recognize PMA as being the life-changing illness that it is. In cases where being classified as being PMA rather than ALS is likely to restrict access to services, it may be preferable to be diagnosed as "slowly progressive ALS" or "lower motor neuron predominant" ALS.

An initial diagnosis of PMA could turn out to be slowly progressive ALS many years later, sometimes even decades after the initial diagnosis. The occurrence of upper motor neurone symptoms such as brisk reflexes, spasticity, or a Babinski sign would indicate a progression to ALS; the correct diagnosis is also occasionally made on autopsy.

The most common causes in young children are birth trauma and a type of cancer called neuroblastoma. The cause of about a third of cases in children is unknown.

Any condition resulting in decreased peripheral sensation, proprioception, and fine motor control:

- Diabetes mellitus neuropathy (the most common in the U.S. today, resulting in destruction of foot and ankle joints), with Charcot joints in 1/600-700 diabetics. Related to long-term poor glucose control.

- Alcoholic neuropathy

- Cerebral palsy

- Leprosy

- Syphilis ("tabes dorsalis"), caused by the organism "Treponema pallidum"

- Spinal cord injury

- Myelomeningocele

- Syringomyelia

- Intra-articular steroid injections

- Congenital insensitivity to pain

- Peroneal muscular atrophy

Chronic paresthesia (Berger's paresthesia, Sinagesia or Bernhardt paresthesia) indicates a problem with the functioning of neurons or poor circulation.

In older individuals, paresthesia is often the result of poor circulation in the limbs (such as in peripheral vascular disease), most often caused by atherosclerosis, the buildup of plaque within artery walls, over decades, with eventual plaque ruptures, internal clots over the ruptures and subsequent clot healing but leaving behind narrowing of the artery openings or closure, both locally and in downstream smaller branches. Without a proper supply of blood and nutrients, nerve cells can no longer adequately send signals to the brain. Because of this, paresthesia can also be a symptom of vitamin deficiency and malnutrition, as well as metabolic disorders like diabetes, hypothyroidism, and hypoparathyroidism. It can also be a symptom of mercury poisoning.

Irritation to the nerve can also come from inflammation to the tissue. Joint conditions such as rheumatoid arthritis, psoriatic arthritis, and carpal tunnel syndrome are common sources of paresthesia. Nerves below the head may be compressed where chronic neck and spine problems exist and can be caused by, among other things, muscle cramps that may be a result of clinical anxiety or excessive mental stress, bone disease, poor posture, unsafe heavy lifting practices or physical trauma such as whiplash. Paresthesia can also be caused simply by putting pressure on a nerve by applying weight (or pressure) to the limb for extended periods of time.

Another cause of paresthesia may be direct damage to the nerves themselves, i.e., neuropathy, which itself can stem from injury or infection such as frostbite or Lyme disease, or may be indicative of a current neurological disorder. Neuropathy is also a side effect of some chemotherapies (see Chemotherapy-induced peripheral neuropathy). Benzodiazepine withdrawal may also cause paresthesia as the drug removal leaves the GABA receptors stripped bare and possibly malformed. Chronic paresthesia can sometimes be symptomatic of serious conditions, such as a transient ischemic attack, or autoimmune diseases such as multiple sclerosis or lupus erythematosus. Exposure to environmental toxins, chemicals used in water treatment and fluoroquinolones can also cause paresthesia. Stroke survivors and those with Traumatic Brain Injury (TBI) may experience paresthesia from damage to the central nervous system.

The Varicella zoster virus disease (shingles) can attack nerves causing numbness instead of pain commonly associated with shingles. A diagnostic evaluation by a medical doctor is necessary to rule these out.

In reality, both of these mechanisms probably play a role in the development of a Charcot joint.