In terms of diagnosis of HNPP measuring nerve conduction velocity may give an indication of the presence of the disease.Other methods via which to ascertain the diagnosis of hereditary neuropathy with liability to pressure palsy are:

- Family history

- Genetic test

- Physical exam(lack of ankle reflex)

A skin biopsy for the measurement of epidermal nerve fiber density is an increasingly common technique for the diagnosis of small fiber peripheral neuropathy. Physicians can biopsy the skin with a 3-mm circular punch tool and immediately fix the specimen in 2% paraformaldehyde lysine-periodate or Zamboni's fixative. Specimens are sent to a specialized laboratory for processing and analysis where the small nerve fibers are quantified by a neuropathologist to obtain a diagnostic result.

This skin punch biopsy measurement technique is called intraepidermal nerve fiber density (IENFD). The following table describes the IENFD values in males and females of a 3 mm biopsy 10-cm above the lateral malleolus (above ankle outer side of leg). Any value measured below the 0.05 Quantile IENFD values per age span, is considered a reliable positive diagnosis for Small Fiber Peripheral Neuropathy.

The diagnosis of small fiber neuropathy often requires ancillary testing. Nerve conduction studies and electromyography are commonly used to evaluate large myelinated sensory and motor nerve fibers, but are ineffective in diagnosing small fiber neuropathies.

Quantitative sensory testing (QST) assesses small fiber function by measuring temperature and vibratory sensation. Abnormal QST results can be attributed to dysfunction in the central nervous system. Furthermore, QST is limited by a patient’s subjective experience of pain sensation. Quantitative sudomotor axon reflex testing (QSART) measures sweating response at local body sites to evaluate the small nerve fibers that innervate sweat glands.

Familial dysautonomia is inherited in an autosomal recessive pattern, which means 2 copies of the gene in each cell are altered. If both parents are shown to be carriers by genetic testing, there is a 25% chance that the child will produce FD. Prenatal diagnosis for pregnancies at increased risk for FD by amniocentesis (for 14–17 weeks) or chorionic villus sampling (for 10–11 weeks) is possible.

Peripheral neuropathy may first be considered when an individual reports symptoms of numbness, tingling, and pain in feet. After ruling out a lesion in the central nervous system as a cause, diagnosis may be made on the basis of symptoms, laboratory and additional testing, clinical history, and a detailed examination.

During physical examination, specifically a neurological examination, those with generalized peripheral neuropathies most commonly have distal sensory or motor and sensory loss, although those with a pathology (problem) of the nerves may be perfectly normal; may show proximal weakness, as in some inflammatory neuropathies, such as Guillain–Barré syndrome; or may show focal sensory disturbance or weakness, such as in mononeuropathies. Classically, ankle jerk reflex is absent in peripheral neuropathy.

A physical examination will involve testing the deep ankle reflex as well as examining the feet for any ulceration. For large fiber neuropathy, an exam will usually show an abnormally decreased sensation to vibration, which is tested with a 128-Hz tuning fork, and decreased sensation of light touch when touched by a nylon monofilament.

Diagnostic tests include electromyography (EMG) and nerve conduction studies (NCSs), which assess large myelinated nerve fibers. Testing for small-fiber peripheral neuropathies often relates to the autonomic nervous system function of small thinly- and unmyelinated fibers. These tests include a sweat test and a tilt table test. Diagnosis of small fiber involvement in peripheral neuropathy may also involve a skin biopsy in which a 3 mm-thick section of skin is removed from the calf by a punch biopsy, and is used to measure the skin intraepidermal nerve fiber density (IENFD), the density of nerves in the outer layer of the skin. Reduced density of the small nerves in the epidermis supports a diagnosis of small-fiber peripheral neuropathy.

Laboratory tests include blood tests for vitamin B-12 levels, a complete blood count, measurement of thyroid stimulating hormone levels, a comprehensive metabolic panel screening for diabetes and pre-diabetes, and a serum immunofixation test, which tests for antibodies in the blood.

A thorough history is essential and should cover family history, diet; drug/toxin exposure social history, including tobacco and alcohol use; and occupational background, with details on whether similar cases exist among coworkers. Treatment of any chronic disease such as pernicious anemia should always be elucidated.

In most cases of nutritional/toxic optic neuropathy, the diagnosis may be obtained via detailed medical history and eye examination. Additionally, supplementary neurological imaging studies, such as MRI or enhanced CT, may be performed if the cause remains unclear.

When the details of the examination and history indicate a familial history of similar ocular or systemic disease, whether or not there is evidence of toxic or nutritional causes for disease, certain genetic tests may be required. Because there are several congenital causes of mitochondrial dysfunction, the patients history, examination, and radiological studies must be examined in order to determine the specific genetic tests required. For example, 90% of cases of Leber’s Hereditary Optic Neuropathy (LHON) are associated with three common mtDNA point mutations (m.3460G>A/MT-ND1, m.11778G>A/MT-ND4, m.14484T>C/MT-ND6) while a wider range of mtDNA mutations (MT-ND1, MT-ND5, MT-ND6; http://www.mitomap.org/) have been associated with overlapping phenotypes of LHON, MELAS, and Leigh syndrome.

There is no current treatment, however management of hereditary neuropathy with liability to pressure palsy can be done via:

- Occupational therapist

- Ankle/foot orthosis

- Wrist splint (medicine)

- Avoid repetitive movements

In 1993, Peter James Dyck divided HSAN I further into five subtypes HSAN IA-E based on the presence of additional features. These features were thought to result from the genetic diversity of HSAN I (i.e. the expression of different genes, different alleles of a single gene, or modifying genes) or environmental factors. Molecular genetic studies later confirmed the genetic diversity of the disease.

Patients with diabetes and proximal (hip, thigh) pain and weakness are often suspected of having diabetic amyotrophy. More definitive diagnosis is commonly made with electrodiagnostic studies including nerve conduction studies (NCS) and electromyogram (EMG). Diabetic amyotrophy is often a diagnosis of exclusion in diabetic patients with a lumbosacral plexopathy for whom no other cause of lumbosacral plexopathy can be determined.

CMT can be diagnosed through symptoms, through measurement of the speed of nerve impulses (nerve conduction studies), through biopsy of the nerve, and through DNA testing. DNA testing can give a definitive diagnosis, but not all the genetic markers for CMT are known. CMT is first noticed when someone develops lower leg weakness, such as foot drop; or foot deformities, including hammertoes and high arches. But signs alone do not lead to diagnosis. Patients must be referred to a physician specialising in neurology or rehabilitation medicine. To see signs of muscle weakness, the neurologist asks patients to walk on their heels or to move part of their leg against an opposing force. To identify sensory loss, the neurologist tests for deep tendon reflexes, such as the knee jerk, which are reduced or absent in CMT. The doctor also asks about family history, because CMT is hereditary. The lack of family history does not rule out CMT, but helps rule out other causes of neuropathy, such as diabetes or exposure to certain chemicals or drugs.

In 2010, CMT was one of the first diseases where the genetic cause of a particular patient's disease was precisely determined by sequencing the whole genome of an affected individual. This was done by the scientists employed by the Charcot Marie Tooth Association (CMTA) Two mutations were identified in a gene, SH3TC2, known to cause CMT. Researchers then compared the affected patient's genome to the genomes of the patient's mother, father, and seven siblings with and without the disease. The mother and father each had one normal and one mutant copy of this gene, and had mild or no symptoms. The offspring that inherited two mutant genes presented fully with the disease.

Genetic testing is performed on a small sample of blood from the tested individual. The DNA is examined with a designed probe specific to the known mutations. The accuracy of the test is above 99%. Dr. Anat Blumenfeld of the Hadasah Medical center in Jerusalem identified chromosome number 9 as the responsible chromosome.

The diagnosis of HSAN I is based on the observation of symptoms described above and is supported by a family history suggesting autosomal dominant inheritance. The diagnosis is also supported by additional tests, such as nerve conduction studies in the lower limbs to confirm a sensory and motor neuropathy. In sporadic cases, acquired neuropathies, such as the diabetic foot syndrome and alcoholic neuropathy, can be excluded by the use of magnetic resonance imaging and by interdisciplinary discussion between neurologists, dermatologists, and orthopedics.

The diagnosis of the disease has been revolutionized by the identification of the causative genes. The diagnosis is now based on the detection of the mutations by direct sequencing of the genes. Nevertheless, the accurate phenotyping of patients remains crucial in the diagnosis. For pregnant patients, termination of pregnancy is not recommended.

HSAN I must be distinguished from hereditary motor and sensory neuropathy (HMSN) and other types of hereditary sensory and autonomic neuropathies (HSAN II-V). The prominent sensory abnormalities and foot ulcerations are the only signs to separate HSAN I from HMSN. HSAN II can be differentiated from HSAN I as it is inherited as an autosomal recessive trait, it has earlier disease onset, the sensory loss is diffused to the whole body, and it has less or no motor symptoms. HSAN III-V can be easily distinguished from HSAN I because of congenital disease onset. Moreover, these types exhibit typical features, such as the predominant autonomic disturbances in HSAN III or congenital loss of pain and anhidrosis in HSAN IV.

Diabetic peripheral neuropathy is the most likely diagnosis for someone with diabetes who has pain in a leg or foot, although it may also be caused by vitamin B deficiency or osteoarthritis. A 2010 review in the Journal of the American Medical Association's "Rational Clinical Examination Series" evaluated the usefulness of the clinical examination in diagnosing diabetic peripheral neuropathy. While the physician typically assesses the appearance of the feet, presence of ulceration, and ankle reflexes, the most useful physical examination findings for large fiber neuropathy are an abnormally decreased vibration perception to a 128-Hz tuning fork (likelihood ratio (LR) range, 16–35) or pressure sensation with a 5.07 Semmes-Weinstein monofilament (LR range, 11–16). Normal results on vibration testing (LR range, 0.33–0.51) or monofilament (LR range, 0.09–0.54) make large fiber peripheral neuropathy from diabetes less likely. Combinations of signs do not perform better than these 2 individual findings. Nerve conduction tests may show reduced functioning of the peripheral nerves, but seldom correlate with the severity of diabetic peripheral neuropathy and are not appropriate as routine tests for the condition.

In terms of the differential diagnosis for polyneuropathy one must look at the following:

Patients with hereditary motor and sensory neuropathies are diagnosed through a physical evaluation that looks for muscle atrophy, weakness, and sensory responses. In addition to this, EMG (electromyography) and motor nerve conduction tests can help clinicians decide what type of motor and sensory neuropathy it is and how severe the disease is. Final confirmation can come through genetic testing.

Congenital insensitivity to pain with anhidrosis (CIPA), also known as hereditary sensory and autonomic neuropathy type IV (HSAN IV), is characterized by insensitivity to pain, anhidrosis (the inability to sweat), and intellectual disability. The ability to sense all pain (including visceral pain) is absent, resulting in repeated injuries including: oral self-mutilation (biting of tongue, lips, and buccal mucosa); biting of fingertips; bruising, scarring, and infection of the skin; multiple bone fractures (many of which fail to heal properly); and recurrent joint dislocations resulting in joint deformity. Sense of touch, vibration, and position are normal. Anhidrosis predisposes to recurrent febrile episodes that are often the initial manifestation of CIPA. Hypothermia in cold environments also occurs. Intellectual disability of varying degree is observed in most affected individuals; hyperactivity and emotional lability are common.

Hereditary sensory neuropathy type IV (HSN4) is a rare genetic disorder characterized by the loss of sensation (sensory loss), especially in the feet and legs and, less severely, in the hands and forearms. The sensory loss is due to abnormal functioning of small, unmyelinated nerve fibers and portions of the spinal cord that control responses to pain and temperature as well as other involuntary or automatic body processes. Sweating is almost completely absent with this disorder. Intellectual disability is usually present.

Type 4, congenital insensitivity to pain with anhidrosis (CIPA), is an autosomal recessive condition and affected infants present with episodes of hyperthermia unrelated to environmental temperature, anhidrosis and insensitivity to pain. Palmar skin is thickened and charcot joints are commonly present. NCV shows motor and sensory nerve action potentials to be normal. The histopathology of peripheral nerve biopsy reveals absent small unmyelinated fibers and mitochondria are abnormally enlarged.

Management of Hereditary sensory and autonomic neuropathy Type 4:

Treatment of manifestations: Treatment is supportive and is best provided by specialists in pediatrics, orthopedics, dentistry, ophthalmology, and dermatology. For anhidrosis: Monitoring body temperature helps to institute timely measures to prevent/manage hyperthermia or hypothermia. For insensitivity to pain: Modify as much as reasonable a child’s activities to prevent injuries. Inability to provide proper immobilization as a treatment for orthopedic injuries often delays healing; additionally, bracing and invasive orthopedic procedures increase the risk for infection. Methods used to prevent injuries to the lips, buccal mucosa, tongue, and teeth include tooth extraction, and/or filing (smoothing) of the sharp incisal edges of teeth, and/or use of a mouth guard. Skin care with moisturizers can help prevent palmar and plantar hyperkeratosis and cracking and secondary risk of infection; neurotrophic keratitis is best treated with routine care for dry eyes, prevention of corneal infection, and daily observation of the ocular surface. Interventions for behavioral, developmental, and motor delays as well as educational and social support for school-age children and adolescents are recommended.

Prevention of secondary complications: Regular dental examinations and restriction of sweets to prevent dental caries; early treatment of dental caries and periodontal disease to prevent osteomyelitis of the mandible. During and following surgical procedures, potential complications to identify and manage promptly include hyper- or hypothermia and inadequate sedation, which may trigger unexpected movement and result in secondary injuries.

The severity of symptoms vary widely even for the same type of CMT. There have been cases of monozygotic twins with varying levels of disease severity, showing that identical genotypes are associated with different levels of severity (see penetrance). Some patients are able to live a normal life and are almost or entirely asymptomatic. A 2007 review stated that "Life expectancy is not known to be altered in the majority of cases".

The diagnosis of polyneuropathies begins with a history and physical examination to ascertain the pattern of the disease process (such as-arms, legs, distal, proximal) if they fluctuate, and what deficits and pain are involved. If pain is a factor, determining where and how long the pain has been present is important, one also needs to know what disorders are present within the family and what diseases the person may have. Although diseases often are suggested by the physical examination and history alone, tests that may be employed include: electrodiagnostic testing, serum protein electrophoresis, nerve conduction studies, urinalysis, serum creatine kinase (CK) and antibody testing (nerve biopsy is sometimes done).

Other tests may be used, especially tests for specific disorders associated with polyneuropathies, quality measures have been developed to diagnose patients with distal symmetrical polyneuropathy (DSP).

While the clinical picture may point towards the diagnosis of the Roussy–Lévy syndrome, the condition can only be confirmed with absolute certainty by carrying out genetic testing in order to identify the underlying mutations.

Five different clinical entities have been described under hereditary sensory and autonomic neuropathies – all characterized by progressive loss of function that predominantly affects the peripheral sensory nerves. Their incidence has been estimated to be about 1 in 25,000.

In terms of the diagnosis of radial neuropathy the following tests/exams can be done to ascertain the condition:

Radial neuropathy is not necessarily permanent. The majority of radial neuropathies due to an acute compressive event (Saturday night palsy) do recover without intervention. If the injury is demyelinating (meaning only the myelin sheath surrounding the nerve is damaged), then full recovery typically occurs within 2–4 weeks. If the injury is axonal (meaning the underlying nerve fiber itself is damaged) then full recovery may take months or years, or may never occur. EMG and nerve conduction studies are typically performed to diagnose the extent and distribution of the damage, and to help with prognosis for recovery.

Charcot–Marie–Tooth disease was first described in 1886 by Jean-Martin Charcot, Pierre Marie, and independently Howard Henry Tooth. In the 1950s, further classification occurred and separated patients into two distinct groups. Group one was characterized by slow nerve conduction velocities and demyelinating neuropathy. Group two was characterized by mostly normal nerve conduction velocities and degeneration of axons. In 1968, HMSN were classified again into seven groups:

The clinical diagnosis is backed up by investigative findings. Citrulline level in blood is decreased. Mitochondrial studies or NARP mtDNA evaluation plays a role in genetic diagnosis which can also be done prenatally.

Diabetic neuropathy encompasses a series of different neuropathic syndromes which can be schematized in the following way:

- Focal and multifocal neuropathies:

- Mononeuropathy

- Amyotrophy, radiculopathy

- Multiple lesions "mononeuritis multiplex"

- Entrapment (e.g. median, ulnar, peroneal)

- Symmetrical neuropathies:

- Acute sensory

- Autonomic

- Distal symmetrical polyneuropathy (DSPN), the diabetic type of which is also known as diabetic peripheral neuropathy (DPN) (most common presentation)