It can be diagnosed clinically in the appropriate context, but may be difficult to confirm radiologically using conventional imaging techniques. Changes are more prominent on MRI than on CT, but often take days or weeks after acute symptom onset to develop. Imaging by MRI typically demonstrates areas of hyperintensity on T2-weighted images.

Diagnosis of Wernicke's encephalopathy or disease is made clinically. Caine et al. in 1997 established criteria that Wernicke's encephalopathy can be diagnosed in any patient with just two or more of the main symptoms noted above. The sensitivity of the diagnosis by the classic triad was 23% but increased to 85% taking two or more of the four classic features. This criteria is challenged because all the cases he studied were alcoholics.

Some consider it sufficient to suspect the presence of the disease with only one of the principal symptoms. Some British hospital protocols suspect WE with any one of these symptoms: confusion, decreased consciousness level (or unconsciousness, stupor or coma), memory loss, ataxia or unsteadiness, ophthalmoplegia or nystagmus, and unexplained hypotension with hypothermia. The presence of only one sign should be sufficient for treatment.

As a much more diverse range of symptoms has been found frequently in patients it is necessary to search for new diagnostic criteria, however Wernicke's encephalopathy remains a clinically-diagnosed condition. Neither the MR, nor serum measurements related to thiamine are sufficient diagnostic markers in all cases. Non-recovery upon supplementation with thiamine is inconclusive.

The sensitivity of MR was 53% and the specificity was 93%. The reversible cytotoxic edema was considered the most characteristic lesion of WE. The location of the lesions were more frequently atypical among non-alcoholics, while typical contrast enhancement in the thalamus and the mammillary bodies was observed frequently associated with alcohol abuse. These abnormalities may include:

- Medial thalami, periaqueductal gray matter, mamillary bodies, and brainstem nuclei edema (Zuccoli G.). Involvement is always bilateral symmetrical. Value of DWI in the diagnosis of WE is minimal. Axial FLAIR MRI images represent the best diagnostic MRI sequence. Contrast material may highlight involvement of the mamillary bodies.

There appears to be very little value for CT scans.

Thiamine can be measured using an erythrocyte transketolase activity assay, or by activation by measurement of in vitro thiamine diphosphate levels. Normal thiamine levels do not necessarily rule out the presence of WE, as this may be a patient with difficulties in intracellular transport.

There are hospital protocols for prevention, supplementing with thiamine in the presence of: history of alcohol misuse or related seizures, requirement for IV glucose, signs of malnutrition, poor diet, recent diarrhea or vomiting, peripheral neuropathy, intercurrent illness, delirium tremens or treatment for DTs, and others. Some experts advise parenteral thiamine should be given to all at-risk patients in the emergency room.

In the clinical diagnosis should be remembered that early symptoms are nonspecific, and it has been stated that WE may present nonspecific findings. There is consensus to provide water-soluble vitamins and minerals after gastric operations.

In some countries certain foods have been supplemented with thiamine, and have reduced WE cases. Improvement is difficult to quantify because they applied several different actions. Avoiding alcohol and having adequate nutrition reduces one of the main risk factors in developing Wernicke-Korsakoff syndrome.

The diagnosis of short-chain acyl-coenzyme A dehydrogenase deficiency is based on the following:

- Newborn screening test

- Genetic testing

- Urine test

Marchiafava-Bignami disease is routinely diagnosed with the use of an MRI due to the fact that the majority of clinical symptoms are non-specific. Before the use of such imaging equipment, it was unable to be diagnosed until autopsy. The patient usually has a history of alcoholism or malnutrition and neurological symptoms are sometimes present and can help lead to a diagnosis. MBD can be told apart from other neural diseases due to the symmetry of the lesions in the corpus callosum as well as the fact that these lesions don’t affect the upper and lower edges.

There are two clinical subtypes of MBD

Type A- Stupor and coma predominate. Radiological imaging shows involvement of the entire corpus callosum. This type is also associated with symptoms of the upper motor neurons.

Type B- This type has normal or only mildly impair mental status and radiological imaging shows partial lesions in the corpus callosum.

The differential diagnosis for short-chain acyl-coenzyme A dehydrogenase deficiency is: ethylmalonic encephalopathy, mitochondrial respiratory chain defects and "multiple" acyl-CoA dehydrogenase deficiency.

In individuals with marked hyperammonemia, a urea cycle disorder is usually high on the list of possible causes. While the immediate focus is lowering the patient's ammonia concentrations, identifying the specific cause of increased ammonia levels is key as well.

Diagnostic testing for OTC deficiency, or any individual with hyperammonemia involves plasma and urine amino acid analysis, urine organic acid analysis (to identify the presence or absence of orotic acid, as well as rule out an organic acidemia) and plasma acylcarnitines (will be normal in OTC deficiency, but can identify some other causes of hyperammonemia). An individual with untreated OTC deficiency will show decreased citrulline and arginine concentrations (because the enzyme block is proximal to these intermediates) and increased orotic acid. The increased orotic acid concentrations result from the buildup of carbamoyl phosphate. This biochemical phenotype (increased ammonia, low citrulline and increased orotic acid) is classic for OTC deficiency, but can also be seen in neonatal presentations of ornithine aminotransferase deficiency. Only severely affected males consistently demonstrate this classic biochemical phenotype.

Heterozygous females can be difficult to diagnose. With the rise of sequencing techniques, molecular testing has become preferred, particularly when the disease causing mutations in the family are known. Historically, heterozygous females were often diagnosed using an allopurinol challenge. In a female with reduced enzyme activity, an oral dose of allopurinol would be metabolized to oxypurinol ribonucleotide, which blocks the pyrimidine biosynthetic pathway. When this induced enzymatic block is combined with reduced physiologic enzyme activity as seen in heterozygotes, the elevation of orotic acid could be used to differentiate heterozygotes from unaffected individuals. This test was not universally effective, as it had both false negative and false positive results.

Ornithine transcarbamylase is only expressed in the liver, thus performing an enzyme assay to confirm the diagnosis requires a liver biopsy. Before molecular genetic testing was commonly available, this was one of the only methods for confirmation of a suspected diagnosis. In cases where prenatal diagnosis was requested, a fetal liver biopsy used to be required to confirm if a fetus was affected. Modern molecular techniques have eliminated this need, and gene sequencing is now the preferred method of diagnosis in asymptomatic family members after the diagnosis has been confirmed in a proband.

A 1999 retrospective study of 74 cases of neonatal onset found that 32 (43%) patients died during their first hyperammonemic episode. Of those who survived, less than 20% survived to age 14. Few of these patients received liver transplants.

To minimise the risk of this condition developing from its most common cause, overly rapid reversal of hyponatremia, the hyponatremia should be corrected at a rate not exceeding 10 mmol/L/24 h or 0.5 mEq/L/h; or 18 m/Eq/L/48hrs; thus avoiding demyelination. No large clinical trials have been performed to examine the efficacy of therapeutic re-lowering of serum sodium, or other interventions sometimes advocated such as steroids or plasma exchange.

Alcoholic patients should receive vitamin supplementation and a formal evaluation of their nutritional status.

Once osmotic demyelination has begun, there is no cure or specific treatment. Care is mainly supportive. Alcoholics are usually given vitamins to correct for other deficiencies. The favourable factors contributing to the good outcome in CPM without hyponatremia were: concurrent treatment of all electrolyte disturbances, early Intensive Care Unit involvement at the advent of respiratory complications, early introduction of feeding including thiamine supplements with close monitoring of the electrolyte changes and input.

Research has led to improved outcomes. Animal studies suggest that inositol reduces the severity of osmotic demyelination syndrome if given before attempting to correct chronic hyponatraemia. Further study is required before using inositol in humans for this purpose.

Treatment is variable depending on individuals. Some treatments work extremely well with some patients and not at all with others. Some treatments include Therapy with thiamine and vitamin B complex. Alcohol consumption should be stopped. Some patients survive, but with residual brain damage and dementia. Others remain in comas that eventually lead to death. Nutritional counseling is also recommended. Treatment is often similar to those administered for Wenicke-Korsakoff syndrome or for alcoholism.

Type A has 21% mortality rate and an 81% long-term disability rate. Type B has a 0% mortality rate and a 19% long-term disability rate.

One of, if not the most common form of organic acidemia, methylmalonic acidemia is not apparent at birth as symptoms usually do not present themselves until proteins are added to the infant's diet. Because of this, symptoms typically manifest anytime within the first year of life. Due to the severity and rapidity in which this disorder can cause complications when left undiagnosed, screening for methylmalonic acidemia is often included in the newborn screening exam.

Because of the inability to properly break down amino acids completely, the byproduct of protein digestion, the compound methylmalonic acid, is found in a disproportionate concentration in the blood and urine of those afflicted. These abnormal levels are used as the main diagnostic criteria for diagnosing the disorder. This disorder is typically determined through the use of a urine analysis or blood panel. The presence of methylmalonic acidemia can also be suspected through the use of a CT or MRI scan or ammonia test, however these tests are by no means specific and require clinical and metabolic/correlation. Elevated levels of ammonia, glycine, and ketone bodies may also be present in the blood and urine.

The prognosis is very poor. Two studies reported typical age of deaths in infancy or early childhood, with the first reporting a median age of death of 2.6 for boys and less than 1 month for girls.

Methylmalonic acidemia has varying diagnoses, treatment requirements and prognoses, which are determined by the specific genetic mutation causing the inherited form of the disorder. The following are the known genotypes responsible for methylmalonic acidemia:

The mut type can further be divided in mut0 and mut- subtypes, with mut0 characterized by a complete lack of methylmalonyl CoA mutase and more severe symptoms and mut- characterized by a decreased amount of mutase activity.

Mut-, cblB, and cblA versions of methylmalonic acidemia have been found to be cobalamin responsive. Mut0 is a nonresponsive variant.

There are no methods for preventing the manifestation of the pathology of MSUD in infants with two defective copies of the BCKD gene. However, genetic counselors may consult with couples to screen for the disease via DNA testing. DNA testing is also available to identify the disease in an unborn child in the womb.

There are several different forms of glycine encephalopathy, which can be distinguished by the age of onset, as well as the types and severity of symptoms. All forms of glycine encephalopathy present with only neurological symptoms, including mental retardation (IQ scores below 20 are common), hypotonia, apneic seizures, and brain malformations.

With the classical, or neonatal presentation of glycine encephalopathy, the infant is born after an unremarkable pregnancy, but presents with lethargy, hypotonia, apneic seizures and myoclonic jerks, which can progress to apnea requiring artificial ventilation, and often death. Apneic patients can regain spontaneous respiration in their second to third week of life. After recovery from the initial episode, patients have intractable seizures and profound mental retardation, remaining developmentally delayed. Some mothers comment retrospectively that they noticed fetal rhythmic "hiccuping" episodes during pregnancy, most likely reflecting seizure episodes in utero. Patients with the infantile form of glycine encephalopathy do not show lethargy and coma in the neonatal period, but often have a history of hypotonia. They often have seizures, which can range in severity and responsiveness to treatment, and they are typically developmentally delayed. Glycine encephalopathy can also present as a milder form with episodic seizures, ataxia, movement disorders, and gaze palsy during febrile illness. These patients are also developmentally delayed, to varying degrees. In the later onset form, patients typically have normal intellectual function, but present with spastic diplegia and optic atrophy.

Transient neonatal hyperglycinemia has been described in a very small number of cases. Initially, these patients present with the same symptoms and laboratory results that are seen in the classical presentation. However, levels of glycine in plasma and cerebrospinal fluid typically normalize within eight weeks, and in five of six cases there were no neurological issues detected at follow-up times up to thirteen years. A single patient was severely retarded at nine months. The suspected cause of transient neonatal hyperglicinemia is attributed to low activity of the glycine cleavage system in the immature brain and liver of the neonate.

On 9 May 2014, the UK National Screening Committee (UK NSC) announced its recommendation to screen every newborn baby in the UK for four further genetic disorders as part of its NHS Newborn Blood Spot Screening programme, including maple syrup urine disease.

Newborn screening for maple syrup urine disease involves analyzing the blood of 1–2 day-old newborns through tandem mass spectrometry. The blood concentration of leucine and isoleucine is measured relative to other amino acids to determine if the newborn has a high level of branched-chain amino acids. Once the newborn is 2–3 days old the blood concentration of branched-chain amino acids like leucine is greater than 1000 µmol/L and alternative screening methods are used. Instead, the newborn’s urine is analyzed for levels of branched-chain alpha-hydroxyacids and alpha-ketoacids.

Clinical signs of PEM are variable depending on the area of the cerebral cortex affected and may include head pressing, dullness, opisthotonos, central blindness, anorexia, muscle tremors, teeth grinding, trismus, salivation, drooling, convulsions, nystagmus, clonic convulsions, and recumbency. Early administration of thiamine may be curative, but if the lesion is more advanced, then surviving animals may remain partially blind and mentally dull.

Alcoholic polyneuropathy is very similar to other axonal degenerative polyneuropathies and therefore can be difficult to diagnose. When alcoholics have sensorimotor polyneuropathy as well as a nutritional deficiency, a diagnosis of alcoholic polyneuropathy is often reached.

To confirm the diagnosis, a physician must rule out other causes of similar clinical syndromes. Other neuropathies can be differentiated on the basis of typical clinical or laboratory features. Differential diagnoses to alcoholic polyneuropathy include amyotrophic lateral sclerosis, beriberi, Charcot-Marie-Tooth disease, diabetic lumbosacral plexopathy, Guillain Barre Syndrome, diabetic neuropathy, mononeuritis multiplex and post-polio syndrome.

To clarify the diagnosis, medical workup most commonly involves laboratory tests, though, in some cases, imaging, nerve conduction studies, electromyography, and vibrometer testing may also be used.

A number of tests may be used to rule out other causes of peripheral neuropathy. One of the first presenting symptoms of diabetes mellitus may be peripheral neuropathy, and hemoglobin A1C can be used to estimate average blood glucose levels. Elevated blood creatinine levels may indicate renal insufficiency and may also be a cause of peripheral neuropathy. A heavy metal toxicity screen should also be used to exclude lead toxicity as a cause of neuropathy.

Alcoholism is normally associated with nutritional deficiencies, which may contribute to the development of alcoholic polyneuropathy. Thiamine, vitamin B-12, and folic acid are vitamins that play an essential role in the peripheral and central nervous system and should be among the first analyzed in laboratory tests. It has been difficult to assess thiamine status in individuals due to difficulties in developing a method to directly assay thiamine in the blood and urine. A liver function test may also be ordered, as alcoholic consumption may cause an increase in liver enzyme levels.

The diagnosis is based on clinical features, with a concomitant decreased blood adenosine deaminase level supporting the diagnosis.

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.

There is a deficiency of malate in patients because fumarase enzyme can't convert fumarate into it therefore treatment is with oral malic acid which will allow the krebs cycle to continue, and eventually make ATP.

A 2001 study followed up on 50 patients. Of these 38% died in childhood while the rest suffered from problems with morbidity.

Rapid diagnosis is important to attempt to prevent further damage to the brain and further neurologic deficits. It is a diagnosis of exclusion, so a full work up for other possible etiologies (hepatic, uremic, infectious, oncologic) should be performed. Screening for heavy metals, as well as other toxins, should be done immediately as those are some of the most common causes and the patient can then remove themselves from the dangerous environment. In addition, a full examination of blood (CBC) and metabolites (CMP) should be done.

A positive diagnosis test for thiamine deficiency can be ascertained by measuring the activity of the enzyme transketolase in erythrocytes (Erythrocyte Transketolase Activation Assay). Thiamine, as well as its phosphate derivatives, can also be detected directly in whole blood, tissues, foods, animal feed, and pharmaceutical preparations following the conversion of thiamine to fluorescent thiochrome derivatives (Thiochrome Assay) and separation by high-performance liquid chromatography (HPLC). In recent reports, a number of Capillary Electrophoresis (CE) techniques and in-capillary enzyme reaction methods have emerged as potential alternative techniques for the determination and monitoring of thiamine in samples.

The normal thiamine concentration in EDTA-blood is about 20-100 µg/l.

Diagnosis of canine phosphofructokinase deficiency is similar to the blood tests used in diagnosis of humans. Blood tests measuring the total erythrocyte PFK activity are used for definitive diagnosis in most cases. DNA testing for presence of the condition is also available.

Treatment mostly takes the form of supportive care. Owners are advised to keep their dogs out of stressful or exciting situations, avoid high temperature environments and strenuous exercise. It is also important for the owner to be alert for any signs of a hemolytic episode. Dogs carrying the mutated form of the gene should be removed from the breeding population, in order to reduce incidence of the condition.