While moderate to severe traumatic brain injury is a risk for ALS, it is unclear if mild traumatic brain injury increases rates.

In 1994 the National Institute for Occupational Safety and Health (NIOSH) reported a nonsignificant increase in nervous system disorders due to four cases of ALS among National Football League (NFL) players. It was unclear if this was due to chance or not. Another study from 2012 also found a possible increase in ALS in NFL football players. An older study did not find an increased risk among high school football players. A 2007 review found an increased risk among soccer players. ALS may also occur more often among the US military veterans however the reason is unknown. This may be due to head injury.

After the 2012 report was released, some NFL players involved in the legal settlement with the NFL complained that the NFL, which initially agreed to pay $765 million, was not doing enough to help players. The judge in the case concurred, and the NFL then agreed to pay an unlimited amount of damages for players found to have ALS, Parkinson's disease, Alzheimer's disease and dementia.

About 5–10% of cases are directly inherited from a person's parents. Overall, first-degree relatives of an individual with ALS have a 1% risk of developing ALS.

A defect on chromosome 21, which codes for superoxide dismutase, is associated with about 20% of familial cases of ALS, or about 2% of ALS cases overall. This mutation is believed to be transmitted in an autosomal dominant manner, and has over a hundred different forms of mutation. The most common ALS-causing mutation is a mutant "SOD1" gene, seen in North America; this is characterized by an exceptionally rapid progression from onset to death. The most common mutation found in Scandinavian countries, D90A-SOD1, is more slowly progressive than typical ALS, and people with this form of the disorder survive for an average of 11 years.

In 2011, a genetic abnormality known as a hexanucleotide repeat was found in a region called C9orf72, which is associated with ALS combined with frontotemporal dementia ALS-FTD, and accounts for some 6% of cases of ALS among white Europeans.

Researchers do not fully understand what causes PLS, although it is thought it could be due to a combination of environmental and genetic factors. Studies are being done to evaluate the possible causes, although linking causality can be difficult due to the relatively low number of people who are diagnosed with PLS.

Juvenile PLS may be caused by the ALS2 gene, although this condition is very rare.

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.

A motor neuron disease (MND) is any of several neurological disorders that selectively affect motor neurons, the cells that control voluntary muscles of the body. They include amyotrophic lateral sclerosis (ALS), hereditary spastic paraplegia (HSP), primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), progressive bulbar palsy (PBP) and pseudobulbar palsy. Spinal muscular atrophies (SMA) are sometimes included in the group by some neurologists but it is different disease with clear genetic cause. They are neurodegenerative in nature and cause increasing disability and eventually, death.

Patients can often live with PLS for many years and very often outlive their neurological disease and succumb to some unrelated condition. There is currently no effective cure, and the progression of symptoms varies. Some people may retain the ability to walk without assistance, but others eventually require wheelchairs, canes, or other assistive devices.

Motor neuron diseases affect either upper motor neurons (UMN) or lower motor neurons (LMN), or both:

People with MMND become progressively more weak with time. Generally, affected individuals survive up to 30 years after they are diagnosed.

The cause of MMND has not yet been determined. There are cases where MMND appears to be inherited. However, no relevant genes have been identified.

MMND affects many cranial nerves, particularly involving the 7th (facial nerve) and 9th to the 12th cranial nerves (in order: glossopharyngeal nerve, vagus nerve, accessory nerve, spinal accessory nerve).

Despite being rarer than ALS, PMA was described earlier, when in 1850 French neurologist François Aran () described 11 cases which he termed "atrophie musculaire progressive". Contemporary neurologist Guillaume-Benjamin-Amand Duchenne de Boulogne also claimed to have described the condition 1 year earlier, although the written report was never found. The condition has been called progressive muscular atrophy (PMA), spinal muscular atrophy (SMA), Aran–Duchenne disease, Duchenne–Aran disease, Aran–Duchenne muscular atrophy, and Duchenne–Aran muscular atrophy. The name "spinal muscular atrophy" is ambiguous as it refers to any of various spinal muscular atrophies, including the autosomal recessive spinal muscular atrophy caused by a genetic defect in the "SMN1" gene.

In lack of pharmacological treatment, people with SMA tend to deteriorate over time. Recently, survival has increased in severe SMA patients with aggressive and proactive supportive respiratory and nutritional support.

The majority of children diagnosed with SMA type 0 and I do not reach the age of IV, recurrent respiratory problems being the primary cause of death. With proper care, milder SMA type I cases (which account for approx. 10% of all SMA1 cases) live into adulthood. Long-term survival in SMA type I is not sufficiently evidenced; however, recent advances in respiratory support seem to have brought down mortality.

In SMA type II, the course of the disease is slower to progress and life expectancy is less than the healthy population. Death before the age of 20 is frequent, although many people with SMA live to become parents and grandparents. SMA type III has normal or near-normal life expectancy if standards of care are followed. Type IV, adult-onset SMA usually means only mobility impairment and does not affect life expectancy.

In all SMA types, physiotherapy has been shown to delay the progress of disease.

Intention tremors are common among individuals with multiple sclerosis (MS). One common symptom of multiple sclerosis is ataxia, a lack of coordinated muscle movement caused by cerebellar lesions characteristic of multiple sclerosis. The disease often destroys physical and cognitive function of individuals.

Intention tremors can be a first sign of multiple sclerosis, since loss or deterioration of motor function and sensitivity are often one of the first symptoms of cerebellar lesions.

Intention tremors have a variety of other recorded causes as well. These include a variety of neurological disorders, such as stroke, alcoholism, alcohol withdrawal, peripheral neuropathy, Wilson's disease, Creutzfeldt–Jakob disease, Guillain–Barré syndrome and fragile X syndrome, as well as brain tumors, low blood sugar, hyperthyroidism, hypoparathyroidism, insulinoma, normal aging, and traumatic brain injury. Holmes tremor, a rubral or midbrain tremor, is another form of tremor that includes intention tremors, among other symptoms. This disease affects the proximal muscles of the head, shoulders, and neck. Tremors of this disease occur at frequencies of 2–4 Hz or more.

Intention tremor is also known to be associated with infections, West Nile virus, rubella, H. influenza, rabies, and varicella. A variety of poisons have been shown to cause intention tremor, including mercury, methyl bromide, and phosphine. In addition, vitamin deficiencies have been linked to intention tremor, especially deficiency in vitamin E. Pharmacological agents such as anti-arrhythmic drugs, anti-epileptic agents, benzodiazepine, cyclosporine, lithium, neuroleptics, and stimulants have been known to cause intention tremor. Some ordinary activities including ingesting too much caffeine, cigarettes, and alcohol, along with stress, anxiety, fear, anger and fatigue

have also been shown to cause intention tremor by negatively affecting the cerebellum, brainstem, or thalamus, as discussed in mechanisms.

Pseudobulbar palsy is the result of damage of motor fibers traveling from the cerebral cortex to the lower brain stem. This damage might arise in the course of a variety of neurological conditions that involve demyelination and bilateral corticobulbar lesions. Examples include:

- Vascular causes: bilateral hemisphere infarction, CADASIL syndrome

- Progressive supranuclear palsy

- Amyotrophic lateral sclerosis

- Parkinson's disease and related multiple system atrophy

- Various motor neuron diseases, especially those involving demyelination

- Multiple sclerosis and other inflammatory disorders

- High brain stem tumors

- Metabolic causes: osmotic demyelination syndrome

- Neurological involvement in Behçet's disease

- Brain trauma

Neuromuscular disease can be caused by autoimmune disorders, genetic/hereditary disorders and some forms of the collagen disorder Ehlers–Danlos Syndrome, exposure to environmental chemicals and poisoning which includes heavy metal poisoning. The failure of the electrical insulation surrounding nerves, the myelin, is seen in certain deficiency diseases, such as the failure of the body's system for absorbing vitamin B-12

Diseases of the motor end plate include myasthenia gravis, a form of muscle weakness due to antibodies against acetylcholine receptor, and its related condition Lambert-Eaton myasthenic syndrome (LEMS). Tetanus and botulism are bacterial infections in which bacterial toxins cause increased or decreased muscle tone, respectively.Muscular dystrophies, including Duchenne's and Becker's, are a large group of diseases, many of them hereditary or resulting from genetic mutations, where the muscle integrity is disrupted, they lead to progressive loss of strength and decreased life span.

Further causes of neuromuscular diseases are :

Inflammatory muscle disorders

- Polymyalgia rheumatica (or "muscle rheumatism") is an inflammatory condition that mainly occurs in the elderly; it is associated with giant-cell arteritis(It often responds to prednisolone).

- Polymyositis is an autoimmune condition in which the muscle is affected.

- Rhabdomyolysis is the breakdown of muscular tissue due to any cause.

Tumors

- Smooth muscle: leiomyoma (benign)

- Striated muscle: rhabdomyoma (benign)

The cause of PBP is unknown. One form of PBP is found to occur within patients that have a CuZn-superoxide dismutase (SOD1) mutation. Progressive bulbar palsy patients that have this mutation are classified with FALS patients, Familial ALS (FALS) accounts for about 5%-10% of all ALS cases and is caused by genetic factors. Within these, about 20-25% are linked to the SOD1 mutation. It is not currently known if and how the decreased SOD1 activity contributes to Progressive Bulbar Palsy or FALS, and studies are being done in patients and transgenic mice to help further understand the impact of this gene on the disease.

A case study was done on a 42-year-old woman who complained of muscle weakness 10 months prior to admission in the hospital. Upon neurological examination, the patient showed muscle atrophy, fasciculation in all limbs and decreased deep tendon reflexes. The patient’s older brother, father, and paternal uncle had previously all died of ALS or an ALS type syndrome. The patient developed Progressive Bulbar Palsy, became dependent on a respirator, and had two episodes of cardiac arrest. The patient died from pneumonia two years after the onset of the disease. After studying the patient, it was found that the patient had a two base pair deletion in the 126th codon in exon 5 of the SOD1 gene. This mutation produced a frameshift mutation, which led to a stop codon at position 131. SOD1 activity was decreased by about 30%. The patient’s histological examination showed severe reduction in lower motor neurons. Upon further study, this case proved to be important because it demonstrated that SOD1 mutations might not effect steady neuropathological changes, and that environmental and genetic factors might affect the phenotype of the SOD1 mutations.

Neuromuscular disease is a very broad term that encompasses many diseases and ailments that impair the functioning of the muscles, either directly, being pathologies of the voluntary muscle, or indirectly, being pathologies of nerves or neuromuscular junctions.

Neuromuscular diseases are those that affect the muscles and/or their direct nervous system control, problems with central nervous control can cause either spasticity or some degree of paralysis (from both lower and upper motor neuron disorders), depending on the location and the nature of the problem. Some examples of central disorders include cerebrovascular accident, Parkinson's disease, multiple sclerosis, Huntington's disease and Creutzfeldt–Jakob disease. Spinal muscular atrophies are disorders of lower motor neuron while amyotrophic lateral sclerosis is a mixed upper and lower motor neuron condition.

Risk factors for benign fasciculations may include the use of anticholinergic drugs over long periods. In particular, these include ethanolamines such as diphenhydramine (brand names Benadryl, Dimedrol, Daedalon and Nytol), used as an antihistamine and sedative, and dimenhydrinate (brand names Dramamine, Driminate, Gravol, Gravamin, Vomex, and Vertirosan) for nausea and motion sickness. Persons with benign fasciculation syndrome (BFS) may experience paraesthesia (especially numbness) shortly after taking such medication; fasciculation episodes begin as the medication wears off.

Stimulants can cause fasciculations directly. These include caffeine, pseudoephedrine (Sudafed), amphetamines, and the asthma bronchodilators salbutamol (brand names Proventil, Combivent, Ventolin). Medications used to treat attention deficit disorder (ADHD) often contain stimulants as well, and are common causes of benign fasciculations. Since asthma and ADHD are much more serious than the fasciculations themselves, this side effect may have to be tolerated by the patient after consulting a physician or pharmacist.

The depolarizing neuromuscular blocker succinylcholine causes fasciculations. It is a normal side effect of the drug's administration, and can be prevented with a small dose of a nondepolarizing neuromuscular blocker prior to the administration of succinylcholine, often 10% of a nondepolarizing NMB's induction dose.

Even if a drug such as caffeine causes fasciculations, that does not necessarily mean it is the only cause. For example, a very slight magnesium deficiency by itself (see below) might not be enough for fasciculations to occur, but when combined with caffeine, the two factors together could be enough.

Progressive Bulbar Palsy is slow in onset, with symptoms starting in most patients around 50–70 years of age. PBP has a life expectancy typically between 6 months and 3 years from onset of first symptoms. It is subtype of the Motor Neurone Diseases (MND) accounting for around 1 in 4 cases. Amyotrophic lateral sclerosis (ALS) is another sub-type. Pure PBP without any EMG or clinical evidence of abnormalities in the legs or arms is possible, albeit extremely rare. Moreover, about twenty-five percent of patients with PBP eventually develop the widespread symptoms common to ALS.

The more severe the type of SMA, the more likely to have nutrition related health issues. Health issues can be; difficulty in feeding, jaw opening, chewing and swallowing. Individuals with such difficulties can be at increase risk of over or undernutrition, failure to thrive and aspiration. Other nutritional issues, espicially in individuals that are non-ambulatory (more severe types of SMA) include; food not passing through the stomach quickly enough, gastric reflux, constipation, vomiting and bloating. Therein, it could be necessary in SMA type I and people with more severe type II to have a feeding tube or gastrostomy. Additionally, metabolic abnormalities resulting from SMA impair β-oxidation of fatty acids in muscles and can lead to organic acidemia and consequent muscle damage, especially when fasting. It is suggested that people with SMA, especially those with more severe forms of the disease, reduce intake of fat and avoid prolonged fasting (i.e., eat more frequently than healthy people) as well as choosing softer foods to avoid aspiration. During an acute illness, especially in children, nutritional problems may first present or can exacerbate an existing problem (example: aspiration) as well as cause other health issues such as electrolyte and blood sugar disturbances.

Chorea-acanthocytosis (ChAc, also called Choreoacanthocytosis), is a rare hereditary disease caused by a mutation of the gene that directs structural proteins in red blood cells. It belongs to a group of four diseases characterized under the name Neuroacanthocytosis. When a patient's blood is viewed under a microscope, some of the red blood cells appear thorny. These thorny cells are called acanthocytes.

Other effects of the disease may include epilepsy, behaviour changes, muscle degeneration, and neuronal degradation similar to Huntington's Disease. The average age of onset of symptoms is 35 years. The disease is incurable and inevitably leads to premature death.

Some more information about Chorea-acanthocytosis is that it is a very complex autosomal recessive adult-onset neurodegenerative disorder. It often shows itself as a mixed movement disorder, in which chorea, tics, dystonia and even parkinsonism may appear as a symptom.

This disease is also characterized by the presence of a few different movement disorders including chorea, dystonia etc.

Chorea-acanthocytosis is considered an autosomal recessive disorder, although a few cases with autosomal dominant inheritance have been noted.

The proposed mechanism of pseudobulbar palsy points to the disinhibition of the motor neurons controlling laughter and crying, proposing that a reciprocal pathway exists between the cerebellum and the brain stem that adjusts laughter and crying responses, making them appropriate to context. The pseudobulbar crying could also be induced by stimulation in the region of the subthalamic nucleus of the brain.

Hereditary motor and sensory neuropathy with proximal dominance (HMSN-P) is an autosomal dominant neurodegenerative disorder that is defined by extensive involuntary and spontaneous muscle contractions, asthenia, and atrophy with distal sensory involvement following. The disease starts presenting typically in the 40s and is succeeded by a slow and continuous onslaught. Muscle spasms and muscle contractions large in number are noted, especially in the earliest stages. The presentation of HMSN-P is quite similar to amyotrophic lateral sclerosis and has common neuropathological findings. Sensory loss happens as the disease progresses, but the amount of sensation lost varies from case to case. There have been other symptoms of HMSN-P reported such as urinary disturbances and a dry cough.

Two large families in Japan have been identified with the disease locus to chromosome 3q. From descendants of Japan, HMSN-P was brought to Brazil, from there it is a pretty isolated disease. Through clinical studies, researchers identified that TFG mutations on chromosome 3q13.2 causes HMSN-P. "The presence of TFG/ubiquitin- and/or TDP-43-immunopositive cytoplasmic inclusions in motor neurons and cytosolic aggregation composed of TDP-43 in cultured cells expressing mutant TFG indicate a novel pathway of motor neuron death"

Inadequate magnesium intake can cause fasciculations, especially after a magnesium loss due to severe diarrhea. Over-exertion and heavy alcohol consumption are also risk factors for magnesium loss. As 70–80% of the adult population does not consume the recommended daily amount of magnesium, inadequate intake may also be a common cause. Treatment consists of increased intake of magnesium from dietary sources such as nuts (especially almonds), bananas, and spinach. Magnesium supplements or pharmaceutical magnesium preparations may also be taken. However, too much magnesium may cause diarrhea, resulting in dehydration and nutrient loss (including magnesium itself, leading to a net loss, rather than a gain). It is well known as a laxative (Milk of Magnesia), though chelated magnesium can largely reduce this effect. Cheaper methods of the chelation process may be unsatisfactory for some people (e.g. mild diarrhea). Magnesium supplements recommend that they be taken only with meals, and not on an empty stomach.

Fasciculation also often occurs during a rest period after sustained stress, such as that brought on by unconsciously tense muscles. Reducing stress and anxiety is therefore another useful treatment.

There is no proven treatment for fasciculations in people with ALS. Among patients with ALS, fasciculation frequency is not associated with the duration of ALS and is independent of the degree of limb weakness and limb atrophy. No prediction of ALS disease duration can be made based on fasciculation frequency alone.

Neurodegeneration is the progressive loss of structure or function of neurons, including death of neurons. Many neurodegenerative diseases – including amyotrophic lateral sclerosis, Parkinson's, Alzheimer's, and Huntington's – occur as a result of neurodegenerative processes. Such diseases are incurable, resulting in progressive degeneration and/or death of neuron cells. As research progresses, many similarities appear that relate these diseases to one another on a sub-cellular level. Discovering these similarities offers hope for therapeutic advances that could ameliorate many diseases simultaneously. There are many parallels between different neurodegenerative disorders including atypical protein assemblies as well as induced cell death. Neurodegeneration can be found in many different levels of neuronal circuitry ranging from molecular to systemic.

Intention tremor, also known as cerebellar tremor, is a dyskinetic disorder characterized by a broad, coarse, and low frequency (below 5 Hz) tremor. The amplitude of an intention tremor increases as an extremity approaches the endpoint of deliberate and visually guided movement (hence the name intention tremor). An intention tremor is usually perpendicular to the direction of movement. When experiencing an intention tremor, one often overshoots or undershoots their target, a condition known as dysmetria. Intention tremor is the result of dysfunction of the cerebellum, particularly on the same side as the tremor in the lateral zone, which controls visually guided movements. Depending on the location of cerebellar damage, these tremors can be either unilateral or bilateral.

A variety of causes have been discovered to date, including damage or degradation of the cerebellum due to neurodegenerative diseases, trauma, tumor, stroke, or toxicity. There is currently no established pharmacological treatment; however, some success has been seen using treatments designed for essential tremors.