BVVL is marked by a number of cranial nerve palsies, including those of the motor components involving the 7th and 9th-12th cranial nerves, spinal motor nerves, and upper motor neurons. Major features of BVVL include facial and neck weakness, fasciculation of the tongue, and neurological disorders from the cranial nerves. The neurological manifestations develop insidiously: they usually begin with sensorineural deafness, progress inexorably to paralysis, and often culminate in respiratory failure. Most mortality in patients has been from either respiratory infections or respiratory muscle paralysis. Pathological descriptions of BVVL include injury and depletion of 3rd-7th cranial nerves, loss of the spinal anterior horn cells, degeneration of Purkinje cells, as well as degeneration of the spinocerebellar and pyramidal tracts. The first symptoms in nearly all cases of BVVL is progressive vision loss and deafness, and the first initial symptoms are seen anywhere from one to three years.

Most cases of deafness are followed by a latent period that can extend anywhere from weeks to years, and this time is usually marked by cranial nerve degeneration. Neurological symptoms of BVVL include optic atrophy, cerebellar ataxia, retinitis pigmentosa, epilepsy and autonomic dysfunction. Non-neurological symptoms can include diabetes, auditory hallucinations, respiratory difficulties, color blindness, and hypertension.

This is the least severe form of nerve injury, with complete recovery. In this case, the axon remains intact, but there is myelin damage causing an interruption in conduction of the impulse down the nerve fiber. Most commonly, this involves compression of the nerve or disruption to the blood supply (ischemia). There is a temporary loss of function which is reversible within hours to months of the injury (the average is 6–9 weeks). Wallerian degeneration does not occur, so recovery does not involve actual regeneration. There is frequently greater involvement of motor than sensory function with autonomic function being retained. In electrodiagnostic testing with nerve conduction studies, there is a normal compound motor action potential amplitude distal to the lesion at day 10, and this indicates a diagnosis of mild neuropraxia instead of axonotmesis or neurotmesis.

Brown-Vialetto-Van-Laere syndrome (BVVL), sometimes known as Brown's Syndrome, is a rare degenerative disorder often initially characterized by progressive sensorineural deafness.

The syndrome most often affects children, adolescents, and young adults. As knowledge of BVVL grows some adult patients have now been diagnosed. There is no known cure, however with prompt treatment the prognosis may be positive with some patients stabilizing and even minor improvements noted in certain cases.

Symptoms typically are onset in the adult years, although, childhood cases have also been observed. Common symptoms include a loss of coordination which is often seen in walking, and slurred speech. ADCA primarily affects the cerebellum, as well as, the spinal cord. Some signs and symptoms are:

HNA is an episodic disorder; it is characterized by episodes generally lasting 1–6 weeks. During an episode, the nerves of the brachial plexus are targeted by the body as antigens, and the body's immune system begins to degenerate the nerves of the brachial plexus. The exact order or location of the nerve degeneration cannot be predicted before an episode. Other areas of the nervous system that have been affected are the phrenic nerves and the recurrent laryngeal. As the nerves lose function, the muscles associated with those nerves begin to atrophy. In brachial plexus degeneration, atrophy may occur in the deltoid muscles. In phrenic nerve degeneration, the diaphragm may be affected. In this case, breathing can be impaired due to a lack of muscle control of the diaphragm. If the recurrent larangyl nerve is targeted, the pharynx will begin to atrophy and voice function may be lost.

Symptoms of HNA may include pain in the back, neck, arms, or shoulders, nerve pulls in the arms or back, muscular atrophy, and weakness.

Transneuronal degeneration can be grouped into two general categories: anterograde and retrograde.

Nerve injury is injury to nervous tissue. There is no single classification system that can describe all the many variations of nerve injury. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve fiber injury and whether there is continuity of the nerve. Usually, however, (peripheral) nerve injury is classified in five stages, based on the extent of damage to both the nerve and the surrounding connective tissue, since supporting glial cells may be involved. Unlike in the central nervous system, neuroregeneration in the peripheral nervous system is possible. The processes that occur in peripheral regeneration can be divided into the following major events: Wallerian degeneration, axon regeneration/growth, and nerve reinnervation. The events that occur in peripheral regeneration occur with respect to the axis of the nerve injury. The proximal stump refers to the end of the injured neuron that is still attached to the neuron cell body; it is the part that regenerates. The distal stump refers to the end of the injured neuron that is still attached to the end of the axon; it is the part of the neuron that will degenerate but that remains in the area toward which the regenerating axon grows. The study of peripheral nerve injury began during the American Civil War and has greatly expanded to the point of using growth-promoting molecules.

Early signs often include weakness of tongue and mouth muscles, fasciculations, and gradually increasing weakness of limb muscles with muscle wasting. Neuromuscular management is supportive, and the disease progresses very slowly, but can eventually lead to extreme disability. Further signs and symptoms include:

Transneuronal degeneration is the death of neurons resulting from the disruption of input from or output to other nearby neurons. It is an active excitotoxic process when a neuron is overstimulated by a neurotransmitter (most commonly glutamate) causing the dysfunction of that neuron (either damaging it or killing it) which drives neighboring neurons into metabolic deficit, resulting in rapid, widespread loss of neurons. This can be either anterograde or retrograde, indicating the direction of the degeneration relative to the original site of damage (see types). There are varying causes for transneuronal degeneration such as brain lesions, disconnection syndromes, respiratory chain deficient neuron interaction, and lobectomies. Although there are different causes, transneuronal degeneration generally results in the same effects (whether they be cellular, dendritic, or axonal) to varying degrees. Transneuronal degeneration is thought to be linked to a number of diseases, most notably Huntington's disease and Alzheimer's disease, and researchers recently have been performing experiments with monkeys and rats, monitoring lesions in different parts of the body to study more closely how exactly the process works.

Individuals with SBMA have muscle cramps and progressive weakness due to degeneration of motor neurons in the brain stem and spinal cord. Ages of onset and severity of manifestations in affected males vary from adolescence to old age, but most commonly develop in middle adult life. The syndrome has neuromuscular and endocrine manifestations.

Distal hereditary motor neuronopathies (distal HMN, dHMN), sometimes also called distal hereditary motor neuropathies, are a genetically and clinically heterogeneous group of motor neuron diseases that result from genetic mutations in various genes and are characterized by degeneration and loss of motor neuron cells in the anterior horn of the spinal cord and subsequent muscle atrophy.

Although they can hardly be distinguished from hereditary motor and sensory neuropathies on the clinical level, dHMNs are considered a separate class of disorders.

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)

In 1993, A. E. Hardnig proposed to classify hereditary motor neuropathies into seven groups based on age at onset, mode of inheritance, and presence of additional features. This initial classification has since been widely adopted and expanded and currently looks as follows:

Note: Acronym "HMN" is also used interchangeably with "DHMN".

Autosomal dominant cerebellar ataxia (ADCA) is a form of spinocerebellar ataxia inherited in an autosomal dominant manner. ADCA is a genetically inherited condition that causes deterioration of the nervous system leading to disorder and a decrease or loss of function to regions of the body.

Degeneration occurs at the cellular level and in certain subtypes results in cellular death. Cellular death or dysfunction causes a break or faulty signal in the line of communication from the central nervous system to target muscles in the body. When there is impaired communication or a lack of communication entirely, the muscles in the body do not function correctly. Muscle control complications can be observed in multiple balance, speech, and motor or movement impairment symptoms. ADCA is divided into three types and further subdivided into subtypes known as SCAs (spinocerebellar ataxias).

FHM signs overlap significantly with those of migraine with aura. In short, FHM is typified by migraine with aura associated with hemiparesis and, in FHM1, cerebellar degeneration. This cerebellar degeneration can result in episodic or progressive ataxia. FHM can also present with the same signs as benign familial infantile convulsions (BFIC) and alternating hemiplegia of childhood. Other symptoms are altered consciousness (in fact, some cases seem related to head trauma), gaze-evoked nystagmus and coma. Aura symptoms, such as numbness and blurring of vision, typically persist for 30–60 minutes, but can last for weeks and months. An attack resembles a stroke, but unlike a stroke, it resolves in time. These signs typically first manifest themselves in the first or second decade of life.

In contrast to amyotrophic lateral sclerosis or primary lateral sclerosis, PMA is distinguished by the "absence" of:

- brisk reflexes

- spasticity

- Babinski's sign

- Emotional lability

Signs and symptoms may not appear for decades after the initial infection and include weakness, diminished reflexes, paresthesias (shooting and burning pains, pricking sensations, and formication), hypoesthesias (abnormally diminished cutaneous, especially tactile, sensory modalities), tabetic gait (locomotor ataxia), progressive degeneration of the joints, loss of coordination, episodes of intense pain and disturbed sensation (including glossodynia), personality changes, urinary incontinence, dementia, deafness, visual impairment, positive Romberg's test, and impaired response to light (Argyll Robertson pupil). The skeletal musculature is hypotonic due to destruction of the sensory limb of the spindle reflex. The deep tendon reflexes are also diminished or absent; for example, the "knee jerk" or patellar reflex may be lacking (Westphal's sign). A complication of tabes dorsalis can be transient neuralgic paroxysmal pain affecting the eyes and the ophthalmic areas, previously called "Pel's crises" after Dutch physician P.K. Pel. Now more commonly called "tabetic ocular crises", an attack is characterized by sudden, intense eye pain, tearing of the eyes and sensitivity to light.

"Tabes dorsalgia" is a related lancinating back pain.

"Tabetic gait" is a characteristic ataxic gait of untreated syphilis where the person's feet slap the ground as they strike the floor due to loss of proprioception. In daylight the person can avoid some unsteadiness by watching their own feet.

Spinocerebellar ataxia (SCA) is one of a group of genetic disorders characterized by slowly progressive incoordination of gait and is often associated with poor coordination of hands, speech, and eye movements. A review of different clinical features among SCA subtypes was recently published describing the frequency of non-cerebellar features, like parkinsonism, chorea, pyramidalism, cognitive impairment, peripheral neuropathy, seizures, among others. As with other forms of ataxia, SCA frequently results in atrophy of the cerebellum, loss of fine coordination of muscle movements leading to unsteady and clumsy motion, and other symptoms.

The symptoms of an ataxia vary with the specific type and with the individual patient. In general, a person with ataxia retains full mental capacity but progressively loses physical control.

As a result of lower motor neurone degeneration, the symptoms of PMA include:

- atrophy

- fasciculations

- muscle weakness

Some patients have symptoms restricted only to the arms or legs (or in some cases just one of either). These cases are referred to as "Flail Arm" (FA) or "Flail Leg" (FL) and are associated with a better prognosis.

People with CIP/CIM have diffuse, symmetric, flaccid muscle weakness. CIP/CIM typically develops in the setting of a critical illness and immobilization, so patients with CIP/CIM are often receiving treatment in the intensive care unit (ICU).

Weakness (motor deficits) occurs in generalized fashion, rather than beginning in one region of the body and spreading. Limb and respiratory (diaphragm) muscles are especially affected. The muscles of the face are usually spared, but in rare cases, the eye muscles may be weakened, leading to ophthalmoplegia.

Respiratory difficulties can be caused by atrophy of the muscles between the ribs (intercostals), atrophy of the diaphragm muscle, and degeneration of the nerve that stimulates the diaphragm (phrenic nerve). This can prolong the time the wean a person off of a breathing machine (mechanical ventilation) by as much as 7 – 13 days.

Deep tendon reflexes may be lost or diminished, and there may be bilateral symmetric flaccid paralysis of the arms and legs. The nervous system manifestations are typically limited to peripheral nerves, as the central nervous system is usually unaffected.

Tabes dorsalis is caused by demyelination by advanced syphilis infection (tertiary syphilis), when the primary infection by the causative spirochete bacterium, "Treponema pallidum", is left untreated for an extended period of time (past the point of blood infection by the organism).

Zenker's degeneration is a severe glassy or waxy hyaline degeneration or necrosis of skeletal muscles in acute infectious diseases ;a prototype of coagulative necrosis.

The condition was named by Friedrich Albert von Zenker. It is a hyaline degeneration of skeletal muscles such as rectus abdominis and diaphragm, and occurs in severe toxaemia as typhoid fever. It is also seen in electrical burns. Grossly the muscles appear pale and friable; microscopically, the muscle fibres are swollen, have a loss of cross striations, and show a hyaline appearance. Rupture and small hemorrhage may complicate the lesion. Coagulative necrosis occurs here.

Spinocerebellar ataxia (SCA), also known as spinocerebellar atrophy or spinocerebellar degeneration, is a progressive, degenerative, genetic disease with multiple types, each of which could be considered a disease in its own right. An estimated 150,000 people in the United States have a diagnosis of spinocerebellar ataxia at any given time. SCA is hereditary, progressive, degenerative, and often fatal. There is no known effective treatment or cure. SCA can affect anyone of any age. The disease is caused by either a recessive or dominant gene. In many cases people are not aware that they carry a relevant gene until they have children who begin to show signs of having the disorder.

A number of terms are used to describe critical illness polyneuropathy, partially because there is often neuropathy and myopathy in the same person, and nerve and muscle degeneration are difficult to distinguish from each other in this condition. Terms used for the condition include: critical illness polyneuromyopathy, critical illness neuromyopathy, and critical illness myopathy and neuropathy (CRIMYNE). Bolton's neuropathy is an older term, which is no longer used.