In dairy breeds, the disease may occur in calves between birth and 4 months of age. In rustic breeds or beef cattle, heifers and young steers up to 12 months of age can be affected. In calves, muscles in upper portion of the front legs and the hind legs are degraded, causing the animal to have a stiff gait and it may have difficulty standing. The disease may also present in the form of respiratory distress.

In lambs, the disease typically occurs between 3 to 8 weeks of age, but may occur in older lambs as well. Progressive paralysis occurs, which is evident through the following symptoms: arched back, difficulty moving and an open shouldered stance. Cardiac failure may occur in two forms: sudden heart failure or gradual cardiac failure characterized by lung anemia that causes death due to suffocation.

Ewes may be given an injection of vitamin E/selenium prior to lambing to prevent deficiencies in lambs. In areas, such as Ontario, where lambs are highly susceptible to the condition, management practices should include vitamin E/selenium injections.

In the US, the Dietary Reference Intake for adults is 55 µg/day. In the UK it is 75 µg/day for adult males and 60 µg/day for adult females. 55 µg/day recommendation is based on full expression of plasma glutathione peroxidase. Selenoprotein P is a better indicator of selenium nutritional status, and full expression of it would require more than 66 µg/day.

Prognosis strongly depends on which subtype of disease it is. Some are deadly in infancy but most are late onset and mostly manageable.

There is currently no cure for the disease but treatments to help the symptoms are available.

It can occur in patients with severely compromised intestinal function, those undergoing total parenteral nutrition, those who have had gastrointestinal bypass surgery, and also in persons of advanced age (i.e., over 90).

People dependent on food grown from selenium-deficient soil may be at risk for deficiency. Increased risk for developing various diseases has also been noted, even when certain individuals lack optimal amounts of selenium, but not enough to be classified as deficient.

For some time now, it has been reported in medical literature that a pattern of side-effects possibly associated with cholesterol-lowering drugs (e.g., statins) may resemble the pathology of selenium deficiency.

Diagnostic procedures that may reveal muscular disorders include direct clinical observations. This usually starts with the observation of bulk, possible atrophy or loss of muscle tone. Neuromuscular disease can also be diagnosed by testing the levels of various chemicals and antigens in the blood, and using electrodiagnostic medicine tests including electromyography (measuring electrical activity in muscles) and nerve conduction studies.

In neuromuscular disease evaluation, it is important to perform musculoskeletal and neurologic examinations. Genetic testing is an important part of diagnosing inherited neuromuscular conditions.

Frail elderly people are at significant risk of post-surgical complications and the need for extended care. Frailty more than doubles the risk of morbidity and mortality from surgery and cardiovascular conditions. Assessment of older patients before elective surgeries can accurately predict the patients' recovery trajectories.

The most widely used frailty scale consists of five items:

- unintentional weight loss >4.5 kg in the past year

- <20th population centile for grip strength

- self-reported exhaustion

- low physical activity such that persons would only rarely undertake a short walk

- slowed walking speed, defined as lowest population quartile on 4 minute walking test.

A healthy person scores 0; a very frail person scores 5. Compared to non-frail elderly people, people with intermediate frailty scores (2 or 3) are twice as likely to have post-surgical complications, spend 50% more time in the hospital, and are three times as likely to be discharged to a skilled nursing facility instead of to their own homes. Frail elderly patients (score of 4 or 5) have even worse outcomes, with the risk of being discharged to a nursing home rising to twenty times the rate for non-frail elderly people.

While the disease manifests early in life in most cases, diagnosis of the disease is often quite delayed. The symptoms that affected patients present vary, but the most common presenting symptoms are gastrointestinal issues such as nausea, vomiting, abdominal pain, and diarrhea, and neurologic or ocular symptoms such as hearing loss, weakness, and peripheral neuropathy. These gastrointestinal symptoms cause patients with MNGIE to be very thin and experience persistent weight loss and this often leads to MNGIE being misdiagnosed as an eating disorder. These symptoms without presentation of disordered eating and warped body image warrant further investigation into the possibility of MNGIE as a diagnosis. Presentation of these symptoms and lack of disordered eating are not enough for a diagnosis. Radiologic studies showing hypoperistalsis, large atonic stomach, dilated duodenum, diverticula, and white matter changes are required to confirm the diagnosis. Elevated blood and urine nucleoside levels are also indicative of MNGIE syndrome. Abnormal nerve conduction as well as analysis of mitochondria from liver, intestines, muscle, and nerve tissue can also be used to support the diagnosis.

A successful treatment for MNGIE has yet to be found, however, symptomatic relief can be achieved using pharmacotherapy and celiac plexus neurolysis. Celiac plexus neurolysis involves interrupting neural transmission from various parts of the gastrointestinal tract. By blocking neural transmission, pain is relieved and gastrointestinal motility increases. Stem cell therapies are currently being investigated as a potential cure for certain patients with the disease, however, their success depends on physicians catching the disease early before too much organ damage has occurred.

The MRI of patients with VWM shows a well defined leukodystrophy. These MRIs display reversal of signal intensity of the white matter in the brain. Recovery sequences and holes in the white matter are also visible. Over time, the MRI is excellent at showing rarefaction and cystic degeneration of the white matter as it is replaced by fluid. To show this change, displaying white matter as a high signal (T2-weighted), proton density, and Fluid attenuated inversion recovery (FLAIR) images are the best approach. T2-weighted images also displaying cerebrospinal fluid and rarefied/cystic white matter. To view the remaining tissue, and get perspective on the damage done (also helpful in determining the rate of deterioration) (T1-weighted), proton density, and FLAIR images are ideal as they show radiating stripe patterns in the degenerating white matter. A failure of MRI images is their ineffectiveness and difficulty in interpretation in infants since the brain has not fully developed yet. Though some patterns and signs may be visible, it is still difficult to conclusively diagnose. This often leads to misdiagnosis in infants particularly if the MRI results in equivocal patterns or because of the high water content in infants' brains. The easiest way to fix this problem is a follow-up MRI in the following weeks. A potentially similar appearance of MRI with white matter abnormalities and cystic changes may be seen in some patients with hypomelanosis of Ito, some forms of Lowe's (oculocerebrorenal) disease, or some of the mucopolysaccharidoses.

Hereditary spastic paraplegias can be classified based on the symptoms; mode of inheritance; the patient’s age at onset; the affected genes; and biochemical pathways involved.

Compartment syndrome is a clinical diagnosis, i.e., no diagnostic test conclusively proves its presence or absence, but direct measurement of the pressure in a fascial compartment, and the difference between this pressure and the blood pressure, may be used to assess its severity. High pressures in the compartment and a small difference between compartment pressure and blood pressure indicate that the blood supply is likely to be insufficient, and that surgical intervention may be needed.

Disseminated intravascular coagulation, another complication of rhabdomyolysis and other forms of critical illness, may be suspected on the basis of unexpected bleeding or abnormalities in hematological tests, such as a decreasing platelet count or prolongation of the prothrombin time. The diagnosis can be confirmed with standard blood tests for DIC, such as D-dimer.

To gain a better understanding of the disease, researchers have retrospectively reviewed medical records of probands and others who were assessed through clinical examinations or questionnaires. Blood samples are collected from the families of the probands for genetic testing. These family members are assessed using their standard medical history, on their progression of Parkinson's like symptoms (Unified Parkinson's Disease Rating Scale), and on their progression of cognitive impairment such as dementia (Folstein Test).

If an underlying muscle disease is suspected, for instance if there is no obvious explanation or there have been multiple episodes, it may be necessary to perform further investigations. During an attack, low levels of carnitine in the blood and high levels of acylcarnitine in blood and urine may indicate a lipid metabolism defect, but these abnormalities revert to normal during convalescence. Other tests may be used at that stage to demonstrate these disorders. Disorders of glycolysis can be detected by various means, including the measurement of lactate after exercise; a failure of the lactate to rise may be indicative of a disorder in glycolysis, while an exaggerated response is typical of mitochondrial diseases. Electromyography (EMG) may show particular patterns in specific muscle diseases; for instance, McArdle's disease and phosphofructokinase deficiency show a phenomenon called "cramp-like contracture". There are genetic tests available for many of the hereditary muscle conditions that predispose to myoglobinuria and rhabdomyolysis.

Muscle biopsy can be useful if an episode of rhabdomyolysis is thought to be the result of an underlying muscle disorder. A biopsy sample taken during an episode is often uninformative, as it will show only evidence of cell death or may appear normal. Taking the sample is therefore delayed for several weeks or months. The histopathological appearance on the biopsy indicates the nature of the underlying disorder. For instance, mitochondrial diseases are characterized by "ragged red fibers". Biopsy sites may be identified by medical imaging, such as magnetic resonance imaging, as the muscles may not be uniformly affected.

Standard MRI scans have been performed on 1.5 Tesla scanners with 5 mm thickness and 5 mm spacing to screen for white matter lesions in identified families. If signal intensities of the MRI scans are higher in white matter regions than in grey matter regions, the patient is considered to be at risk for HDLS, although a number of other disorders can also produce white matter changes and the findings are not diagnostic without genetic testing or pathologic confirmation.

In terms of treatment for neuromuscular diseases (NMD), "exercise" might be a way of managing them, as NMD individuals would gain muscle strength. In a study aimed at results of exercise, in muscular dystrophy and Charcot-Marie-Tooth disease, the later benefited while the former did not show benefit; therefore, it depends on the disease Other management routes for NMD should be based on medicinal and surgical procedures, again depending on the underlying cause.

This disease is unusually difficult to diagnose. Patients often report years of wrong diagnosis and treatments that made them worse instead of better. Part of this may be that migraines are present in up to 50% of patients and can cause a confusing array of symptoms including headaches, speech difficulties and visual, auditory or sensory auras. DNA testing is available for only a half dozen common gene mutations, while dozens of known mutations are possible but are not routinely tested. Electromyography (EMG) findings are not specific but the McManis Protocol, also called the Compound Muscle Amplitude Potential test (CMAP)can be used by a skilled neurologist capable of utilizing the EMG, which can give assistance in diagnosing several of these PP disorders. The old glucose/insulin provocative testing can cause life-threatening symptoms and should not be used.

Also of note is that potassium levels do "not" have to range outside of normal limits to cause serious, even life-threatening paralysis. These diseases are "not" the same as having a very low level of potassium (hypokalemia) or high potassium (hyperkalemia) and must not be treated as such. The total body store of potassium is usually normal; it is just in the wrong place.

The individual was examined at age 32, but he stated that he started noting differences 5 years before. He noticed sexual impotency, social isolation, unexplained aggression and sadness, loss of motivation, inert laughs, auditory hallucinations, thought insertion, delusions, and imperative commenting. He showed very minimal physical impairments, commonly seen in child-onsets. However, his MRI showed characteristic signs of VWM disease.

Initial diagnosis of HSPs relies upon family history, the presence or absence of additional signs and the exclusion of other nongenetic causes of spasticity, the latter being particular important in sporadic cases.

Cerebral and spinal MRI is an important procedure performed in order to rule out other frequent neurological conditions, such as multiple sclerosis, but also to detect associated abnormalities such as cerebellar or corpus callosum atrophy as well as white matter abnormalities. Differential diagnosis of HSP should also exclude spastic diplegia which presents with nearly identical day-to-day effects and even is treatable with similar medicines such as baclofen and orthopedic surgery; at times, these two conditions may look and feel so similar that the only "perceived" difference may be HSP's hereditary nature versus the explicitly non-hereditary nature of spastic diplegia (however, unlike spastic diplegia and other forms of spastic cerebral palsy, HSP cannot be reliably treated with selective dorsal rhizotomy).

Ultimate confirmation of HSP diagnosis can only be provided by carrying out genetic tests targeted towards known genetic mutations.

One drug in test seemed to prevent the type of muscle loss that occurs in immobile, bedridden patients.

Testing on mice showed that it blocked the activity of a protein present in the muscle that is involved in muscle atrophy. However, the drug's long-term effect on the heart precludes its routine use in humans, and other drugs are being sought.

Muscle weakness, also known as muscle fatigue, (or "lack of strength") refers to the inability to exert force with one's skeletal muscles. Weakness often follows muscle atrophy and a decrease in activity, such as after a long bout of bedrest as a result of an illness. There is also a gradual onset of muscle weakness as a result of sarcopenia - the age-related loss of skeletal muscle.

A test of strength is often used during a diagnosis of a muscular disorder before the etiology can be identified. Such etiology depends on the type of muscle weakness, which can be true or perceived as well as variable topically. True weakness is substantial, while perceived rather is a sensation of having to put more effort to do the same task. On the other hand, various topic locations for muscle weakness are central, neural and peripheral. Central muscle weakness is an overall exhaustion of the whole body, while peripheral weakness is an exhaustion of individual muscles. Neural weakness is somewhere between.

A detailed family history should be obtained from at least three generations. In particularly a history to determine if there has been any neonatal and childhood deaths: Also a way to determine if any one of the family members exhibit any of the features of the multi-system disease. Specifically if there has been a maternal inheritance, when the disease is transmitted to females only, or if there is a family member who experienced a multi system involvement such as: Brain condition that a family member has been record to have such asseizures, dystonia, ataxia, or stroke like episodes.The eyes with optic atrophy, the skeletal muscle where there has been a history of myalgia, weakness or ptosis. Also in the family history look for neuropathy and dysautonomia, or observe heart conditions such ascardiomyopathy. The patients history might also exhibit a problem in their kidney, such as proximal nephron dysfunction. An endocrine condition, for example diabetes and hypoparathyroidism. The patient might have also had gastrointestinal condition which could have been due to liver disease, episodes of nausea or vomiting. Multiple lipomas in the skin, sideroblastic anemia and pancytopenia in the metabolic system or short stature might all be examples of patients with possible symptoms of MERRF disease.

The degeneration of white matter, which shows the degeneration of myelin, can be seen in a basic MRI and used to diagnose leukodystrophies of all types. T-1 and T-2 weighted FLAIR images are the most useful. FLAIR stands for fluid-attenuated inversion recovery. Electrophysiological and other kinds of laboratory testing can also be done. In particular, nerve conduction velocity is looked at to distinguish between leukodystrophy and other demyelinating diseases, as well as to distinguish between individual leukodystrophies. For example, individuals with X-ALD have normal conduction velocities, while those with Krabbe disease or metachromatic leukodystrophy have abnormalities in their conduction velocities. Next generation multigene sequencing panels for undifferentiated leukodystrophy can now be offered for rapid molecular diagnosis after appropriate genetic counselling.

Diagnosis of tumefactive MS is commonly carried out using magnetic resonance imaging (MRI) and proton MR spectroscopy (H-MRS). Diagnosis is difficult as tumefactive MS may mimic the clinical and MRI characteristics of a glioma or a cerebral abscess. However, as compared to tumors and abscesses, tumefactive lesions have an open-ring enhancement as opposed to a complete ring enhancement. Even with this information, multiple imaging technologies have to be used together with biochemical tests for accurate diagnosis of tumefactive MS.

Tumefactive demyelination is distinguished from tumor by the presence of multiple lesions, absence of cortical involvement, and decrease in lesion size or detection of new lesions on serial imaging

Although no cure currently exists, there is hope in treatment for this class of hereditary diseases with the use of an embryonic mitochondrial transplant.