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).

Accurate diagnosis of these Parkinson-plus syndromes is improved when precise diagnostic criteria are used. Since diagnosis of individual Parkinson-plus syndromes is difficult, the prognosis is often poor. Proper diagnosis of these neurodegenerative disorders is important as individual treatments vary depending on the condition. The nuclear medicine SPECT procedure using I-IBZM, is an effective tool in the establishment of the differential diagnosis between patients with PD and Parkinson-plus syndromes.

The types of imaging techniques that are most prominently utilized when studying and/or diagnosing CBD are:

- magnetic resonance imaging (MRI)

- single-photon emission computed tomography (SPECT)

- fluorodopa positron emission tomography (FDOPA PET)

Developments or improvements in imaging techniques provide the future possibility for definitive clinical diagnosis prior to death. However, despite their benefits, information learned from MRI and SPECT during the beginning of CBD progression tend to show no irregularities that would indicate the presence of such a neurodegenerative disease. FDOPA PET is used to study the efficacy of the dopamine pathway.

Despite the undoubted presence of cortical atrophy (as determined through MRI and SPECT) in individuals experiencing the symptoms of CBD, this is not an exclusive indicator for the disease. Thus, the utilization of this factor in the diagnosis of CBD should be used only in combination with other clinically present dysfunctions.

Diagnosis of MSA can be challenging because there is no test that can definitively make or confirm the diagnosis in a living patient. Clinical diagnostic criteria were defined in 1998 and updated in 2007. Certain signs and symptoms of MSA also occur with other disorders, such as Parkinson's disease, making the diagnosis more difficult.

Both MRI and CT scanning frequently show a decrease in the size of the cerebellum and pons in those with cerebellar features. The putamen is hypodense on T2-weighted MRI and may show an increased deposition of iron in Parkinsonian form. In cerebellar form, a "hot cross" sign has been emphasized; it reflects atrophy of the pontocereballar fibers that manifest in T2 signal intensity in atrophic pons.

A definitive diagnosis can only be made pathologically on finding abundant glial cytoplasmic inclusions in the central nervous system.

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.

One of the most significant problems associated with CBD is the inability to perform a definitive diagnosis while an individual exhibiting the symptoms associated with CBD is still alive. A clinical diagnosis of CBD is performed based upon the specified diagnostic criteria, which focus mainly on the symptoms correlated with the disease. However, this often results in complications as these symptoms often overlap with numerous other neurodegenerative diseases. Frequently, a differential diagnosis for CBD is performed, in which other diseases are eliminated based on specific symptoms that do not overlap. However, some of the symptoms of CBD used in this process are rare to the disease, and thus the differential diagnosis cannot always be used.

Postmortem diagnosis provides the only true indication of the presence of CBD. Most of these diagnoses utilize the Gallyas-Braak staining method, which is effective in identifying the presence of astroglial inclusions and coincidental tauopathy.

Genetic testing can confirm a neuroferritinopathy diagnosis. A diagnosis can be made by analyzing the protein sequences of affected individuals and comparing them to known neuroferritinopathy sequences.

Blood tests usually come back normal in affected individuals, so they do not serve as a reliable means of diagnosis. Blood tests can show low serum ferritin levels. However, this is unreliable as method of diagnosis, as some patients show typical serum ferritin levels even at the latest stages of neuroferritinopathy. Cerebral spinal fluid tests also are typically normal.

Ferritin found in the skin, liver, kidney, and muscle tissues may help in diagnosing neuroferritinopathy. More cytochrome c oxidase-negative fibers are also often found in the muscle biopsies of affected individuals.

It is possible to detect the signs of Alexander disease with magnetic resonance imaging (MRI), which looks for specific changes in the brain that may be tell-tale signs for the disease. It is even possible to detect adult-onset Alexander disease with MRI. Alexander disease may also be revealed by genetic testing for the known cause of Alexander disease. A rough diagnosis may also be made through revealing of clinical symptoms including, enlarged head size, along with radiological studies, and negative tests for other leukodystrophies.

The confirmatory diagnosis is made via brain biopsy, however, other tests can be used to help such as MRI, EEG, CT, as well as the physical exam and history

A neurological examination would show evidence of muscle rigidity; weakness; and abnormal postures, movements, and tremors. If other family members are also affected, this may help determine the diagnosis. Genetic tests can confirm an abnormal gene causing the disease. However, this test is not yet widely available. Other movement disorders and diseases must be ruled out. Individuals exhibiting any of the above listed symptoms are often tested using MRI (Magnetic Resonance Imaging) for a number of neuro-related disorders. As PKAN is a disease prominently evident in the brain, MRIs are very useful in making a sound diagnosis. An MRI usually shows iron deposits in the basal ganglia. Development of diagnostic criteria continues in the hope of further separating PKAN from other forms of neurodegenerative diseases featuring NBIA.

Microscopic features of PKAN include:

- Iron granules

- Spheroid bodies

- Lewy bodies within neurons

There is no cure or treatment for GSS. It can, however, be identified through genetic testing. GSS is the slowest to progress among human prion diseases. Duration of illness can range from 3 months to 13 years, with an average duration of 5 or 6 years.

Computed tomography (CT) scans of people with PD usually appear normal. MRI has become more accurate in diagnosis of the disease over time, specifically through iron-sensitive T2* and SWI sequences at a magnetic field strength of at least 3T, both of which can demonstrate absence of the characteristic 'swallow tail' imaging pattern in the dorsolateral substantia nigra. In a meta-analysis, absence of this pattern was 98% sensitive and 95% specific for the disease. Diffusion MRI has shown potential in distinguishing between PD and Parkinson plus syndromes, though its diagnostic value is still under investigation. CT and MRI are also used to rule out other diseases that can be secondary causes of parkinsonism, most commonly encephalitis and chronic ischemic insults, as well as less frequent entities such as basal ganglia tumors and hydrocephalus.

Dopamine-related activity in the basal ganglia can be directly measured with PET and SPECT scans. A finding of reduced dopamine-related activity in the basal ganglia can rule out drug-induced parkinsonism, but reduced basal ganglia dopamine-related activity is seen in both PD and the Parkinson-plus disorders so these scans are not reliable in distinguishing PD from other neurodegenerative causes of parkinsonism.

The prognosis is generally poor. With early onset, death usually occurs within 10 years from the onset of symptoms. Individuals with the infantile form usually die before the age of 7. Usually, the later the disease occurs, the slower its course is.

FXTAS can be diagnosed using a combination of molecular, clinical, and radiological findings. In order for individuals to acquire FXTAS, they must first be permutation carriers, having between 55-200 CGG trinucleotide repeat expansion of the FMR1 gene. A definite, probable, or possible diagnosis of FXTAS can be assigned based on a clinician's confidence based on combined clinical or radiological findings in conjunction with the molecular permutation.

Clinical findings are divided into major and minor symptoms. Major symptoms include intention tremor and gait ataxia. Minor symptoms such as parkinsonism, short-term memory deficit, and executive function decline can further contribute to a diagnosis of FXTAS. Radiological findings are similarly divided into major and minor categories. As patients with FXTAS can have distinct brain scans from other movement disorders, a scan showing white matter lesions of the middle cerebellar peduncle is a major finding that can be attributed to FXTAS. Overall or generalized brain tissue atrophy and cerebral white matter lesions can also be minor indicators for a diagnosis.

For a definite diagnosis to be made, a major radiological finding and one major clinical finding must be present. Probable diagnosis can be made off either a major radiological finding and a minor clinical finding or two major clinical findings alone. The possible category for diagnosis can be made with a minor radiological finding and a major clinical finding.

Parkinson-plus syndromes are usually more rapidly progressive and less likely to respond to antiparkinsonian medication than PD. However, the additional features of the diseases may respond to medications not used in PD.

Current therapy for Parkinson-plus syndromes is centered around a multidisciplinary treatment of symptoms.

These disorders have been linked to pesticide exposure.

A physician will initially assess for Parkinson's disease with a careful medical history and neurological examination. People may be given levodopa, with any resulting improvement in motor impairment helping to confirm the PD diagnosis. The finding of Lewy bodies in the midbrain on autopsy is usually considered final proof that the person had PD. The clinical course of the illness over time may reveal it is not Parkinson's disease, requiring that the clinical presentation be periodically reviewed to confirm accuracy of the diagnosis.

Other causes that can secondarily produce parkinsonism are stroke and drugs. Parkinson plus syndromes such as progressive supranuclear palsy and multiple system atrophy must be ruled out. Anti-Parkinson's medications are typically less effective at controlling symptoms in Parkinson plus syndromes. Faster progression rates, early cognitive dysfunction or postural instability, minimal tremor or symmetry at onset may indicate a Parkinson plus disease rather than PD itself. Genetic forms with an autosomal dominant or recessive pattern of inheritance are sometimes referred to as familial Parkinson's disease or familial parkinsonism.

Medical organizations have created diagnostic criteria to ease and standardize the diagnostic process, especially in the early stages of the disease. The most widely known criteria come from the UK Queen Square Brain Bank for Neurological Disorders and the U.S. National Institute of Neurological Disorders and Stroke. The Queen Square Brain Bank criteria require slowness of movement (bradykinesia) plus either rigidity, resting tremor, or postural instability. Other possible causes of these symptoms need to be ruled out. Finally, three or more of the following supportive features are required during onset or evolution: unilateral onset, tremor at rest, progression in time, asymmetry of motor symptoms, response to levodopa for at least five years, clinical course of at least ten years and appearance of dyskinesias induced by the intake of excessive levodopa.

When PD diagnoses are checked by autopsy, movement disorders experts are found on average to be 79.6% accurate at initial assessment and 83.9% accurate after they have refined their diagnosis at a follow-up examination. When clinical diagnoses performed mainly by nonexperts are checked by autopsy, average accuracy is 73.8%. Overall, 80.6% of PD diagnoses are accurate, and 82.7% of diagnoses using the Brain Bank criteria are accurate.

A task force of the International Parkinson and Movement Disorder Society (MDS) has proposed diagnostic criteria for Parkinson’s disease as well as research criteria for the diagnosis of prodromal disease, but these will require validation against the more established criteria.

There is no cure for GSS, nor is there any known treatment to slow the progression of the disease. However, therapies and medication are aimed at treating or slowing down the effects of the symptoms. Their goal is to try to improve the patient's quality of life as much as possible. Despite there being no cure for GSS, it is possible to undergo testing for the presence of the underlying genetic mutation. Testing for GSS involves a blood and DNA examination in order to attempt to detect the mutated gene at certain codons. If the genetic mutation is present, the patient will eventually be afflicted by GSS, and, due to the genetic nature of the disease, the offspring of the patient are predisposed to a higher risk of inheriting the mutation.

Protein function tests that demonstrate a reduce in chorein levels and also genetic analysis can confirm the diagnosis given to a patient. For a disease like this it is often necessary to sample the blood of the patient on multiple occasions with a specific request given to the haematologist to examine the film for acanthocytes. Another point is that the diagnosis of the disease can be confirmed by the absence of chorein in the western blot of the erythrocyte membranes.

MSA usually progresses more quickly than Parkinson's disease. There is no remission from the disease. The average remaining lifespan after the onset of symptoms in patients with MSA is 7.9 years. Almost 80% of patients are disabled within five years of onset of the motor symptoms, and only 20% survive past 12 years. Rate of progression differs in every case and speed of decline may vary widely in individual patients.

O’Sullivan and colleagues (2008) identified early autonomic dysfunction to be the most important early clinical prognostic feature regarding survival in MSA. Patients with concomitant motor and autonomic dysfunction within three years of symptom onset had a shorter survival duration, in addition to becoming wheelchair dependent and bed-ridden at an earlier stage than those who developed these symptoms after three years from symptom onset. Their study also showed that when patients with early autonomic dysfunction develop frequent falling, or wheelchair dependence, or severe dysphagia, or require residential care, there is a shorter interval from this point to death.

Diagnosis of Jansky–Bielschowsky disease is increasingly based on assay of enzyme activity and molecular genetic testing. Thirteen pathogenic candidate genes—PPT1, TPP1, CLN3, CLN5, CLN6, MFSD8, CLN8, CTSD, DNAJC5, CTSF, ATP13A2 GRN, KCTD7—are associated with the development of the disease. Patients with Jansky–Bielschowsky disease typically have up to 50% reduced lysosomal enzymes, and thus an enzyme activity assay is a quick and easy diagnostic test.

Vision impairment is an early symptom of Jansky–Bielschowsky disease, and so an eye exam is another common diagnostic tool. During the eye exam, loss of cells within the eye would indicate the presence of the disease however more tests are needed for a complete diagnosis.

Other common diagnostic tests include:

- Blood or urine test: Elevated levels of the chemical dolichol found in the urine is typical of individuals with the disease, as well as the presence of vacuolated lymphocytes in the blood.

- Skin or tissue sampling: Microscopy of skin could be used to observe lipopigment aggregation.

- CT scan or MRI: Visualization of the brain would be able to detect areas of cerebral atrophy.

Definitive diagnosis of FTDP-17 requires a combination of characteristic clinical and pathological features and molecular genetic analysis. Genetic counseling should be offered to affected and at-risk individuals; for most subtypes, penetrance is incomplete.

In regards to the diagnosis of spinal and bulbar muscular atrophy, the "AR Xq12" gene is the focus. Many mutations are reported and identified as missense/nonsense, that can be identified with 99.9% accuracy. Test for this gene in the majority of affected patients yields the diagnosis.

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.