Clinical features of CRPS have been found to be inflammation resulting from the release of certain pro-inflammatory chemical signals from the nerves, sensitized nerve receptors that send pain signals to the brain, dysfunction of the local blood vessels' ability to constrict and dilate appropriately, and maladaptive neuroplasticity.

The signs and symptoms of CRPS usually initially manifest near the site of a (typically minor) injury. The most common symptoms are pain sensations, including burning, stabbing, grinding, and throbbing. Moving or touching the limb is often intolerable. The patient may also experience muscle spasms; local swelling; extreme sensitivity to things such as wind and water, touch and vibrations; abnormally increased sweating; changes in skin temperature (usually hot but sometimes cold) and color (bright red or a reddish violet); softening and thinning of bones; joint tenderness or stiffness; changes in nail and hair growth and/or restricted or painful movement. Drop attacks (falls), almost fainting, and fainting spells are infrequently reported, as are visual problems. The symptoms of CRPS vary in severity and duration. Since CRPS is a systemic problem, potentially any organ can be affected.

The pain of CRPS is continuous although varies in severity. It is widely recognized that it can be heightened by emotional or physical stress.

Previously it was considered that CRPS had three stages; it is now believed that people affected by CRPS do not progress through these stages sequentially. These stages may not be time-constrained and could possibly be event-related, such as ground-level falls or re-injuries of previously damaged areas. Thus, rather than a progression of CRPS from bad to worse, it is now thought, instead, that such individuals are likely to have one of the three following types of disease progression:

1. "Stage" one is characterized by severe, burning pain at the site of the injury, muscle spasms, joint stiffness, restricted mobility, rapid hair and nail growth, and vasospasm. The vasospasm is that which causes the changes in the color and temperature of the skin. Some may experience hyperhydrosis (increased sweating). In mild cases this stage lasts a few weeks, in which it can subside spontaneously or respond rapidly to treatment (physical therapy, pain specialist).

2. "Stage" two is characterized by more intense pain. Swelling spreads, hair growth diminishes, nails become cracked, brittle, grooved and spotty, osteoporosis becomes severe and diffuse, joints thicken, and muscles atrophy.

3. "Stage" three is characterized by irreversible changes in the skin and bones, while the pain becomes unyielding and may involve the entire limb. There is marked muscle atrophy, severely limited mobility of the affected area, and flexor tendon contractions (contractions of the muscles and tendons that flex the joints). Occasionally the limb is displaced from its normal position, and marked bone softening and thinning is more dispersed.

Complex regional pain syndrome (CRPS), also known as reflex sympathetic dystrophy (RSD), is a long term pain syndrome that often worsens with time. It is characterized by severe pain out of proportion to the original injury and is often accompanied by sensitivity, swelling, and changes in the skin. It may initially affect one limb and then spread throughout the body; 35% of affected people report symptoms throughout their whole body.

The cause of CRPS is unknown though CRPS is associated with dysregulation of the central nervous system and autonomic nervous system resulting in abnormal temperature control and pain of the affected limb(s) resulting in functional impairment and disability. Precipitating factors include injury and surgery, although there are cases where no identifiable injury had occurred at the original site. CRPS is not caused by psychological factors, yet the constant pain and reduced quality of life are known to cause psychological problems (such as increased depression and anxiety). Although "research does not reveal support for specific personality or psychopathology predictors of the condition," CRPS is associated with psychosocial effects, including impaired social and occupational function. It is classified as an amplified musculoskeletal pain syndrome.

Treatment involves a multidisciplinary approach involving medications, physical and occupational therapy, psychological treatments, and neuromodulation. Despite this, the results are often unsatisfactory, especially if treatment is delayed.

The most prominent symptoms of erythromelalgia are episodes of erythema, swelling, a painful deep-aching of the soft tissue (usually either radiating or shooting) and tenderness, along with a painful burning sensation primarily in the extremities. These symptoms are often symmetric and affect the lower extremities more frequently than the upper extremities. Symptoms may also affect the ears and face. For secondary erythromelalgia, attacks typically precede and are precipitated by the underlying primary condition. For primary erythromelalgia, attacks can last from an hour to months at a time and occur infrequently to frequently with multiple times daily. Common triggers for these episodes are exertion, heating of the affected extremities, and alcohol or caffeine consumption, and any pressure applied to the limbs. In some patients sugar and even melon consumption have also been known to provoke attacks. Many of those with primary erythromelalgia avoid wearing shoes or socks as the heat this generates is known to produce erythromelalgia attacks. Raynaud's phenomenon often coexists in patients with Erythromelalgia. Symptoms may present gradually and incrementally, sometimes taking years to become intense enough for patients to seek medical care. In other cases symptoms emerge full blown with onset.

This syndrome can begin with severe shoulder or arm pain followed by weakness and numbness. Those who suffer from Parsonage–Turner experience acute, sudden-onset pain radiating from the shoulder to the upper arm. Affected muscles become weak and atrophied, and in advanced cases, paralyzed. Occasionally, there will be no pain and just paralysis, and sometimes just pain, not ending in paralysis. MRI may assist in diagnosis. Scapular winging is commonly seen.

Phantom pain involves the sensation of pain in a part of the body that has been removed.

There are various types of sensations that may be felt:

- Sensations related to the phantom limb's posture, length and volume e.g. feeling that the phantom limb is behaving just like a normal limb like sitting with the knee bent or feeling that the phantom limb is as heavy as the other limb. Sometimes, an amputee will experience a sensation called telescoping. This is the feeling that the phantom limb is gradually shortening over time.

- Sensations of movement (e.g. feeling that the phantom foot is moving).

- Sensations of touch, temperature, pressure and itchiness. Many amputees report of feeling heat, tingling, itchiness, and pain.

Parsonage-Turner involves neuropathy of the suprascapular nerve in 97% of cases, and variably involves the axillary and subscapular nerves. As such, the muscles usually involved are the supraspinatus and infraspinatus, which are both innervated by the suprascapular nerve. Involvement of the deltoid is more variable, as it is innervated by the axillary nerve.

Erythromelalgia, formerly known as Mitchell's disease (after Silas Weir Mitchell), is a rare vascular peripheral pain disorder in which blood vessels, usually in the lower extremities or hands, are episodically blocked (frequently on and off daily), then become hyperemic and inflamed. There is severe burning pain (in the small fiber sensory nerves) and skin redness. The attacks are periodic and are commonly triggered by heat, pressure, mild activity, exertion, insomnia or stress. Erythromelalgia may occur either as a primary or secondary disorder (i.e. a disorder in and of itself or a symptom of another condition). Secondary erythromelalgia can result from small fiber peripheral neuropathy of any cause, polycythemia vera, essential thrombocytosis, hypercholesterolemia, mushroom or mercury poisoning, and some autoimmune disorders. Primary erythromelalgia is caused by mutation of the voltage-gated sodium channel α-subunit gene "SCN9A".

In 2004 erythromelalgia became the first human disorder in which it has been possible to associate an ion channel mutation with chronic neuropathic pain; when its pathophysiology was initially published in the Journal of Medical Genetics. Conversely, in December 2006 a University of Cambridge team reported an SCN9A mutation that resulted in a complete lack of pain sensation in a Pakistani street performer and some of his family members. He felt no pain, walked on hot coals and stabbed himself to entertain crowds.

Most patients diagnosed with cubital tunnel syndrome have advanced disease (atrophy, static numbness, weakness) that might reflect permanent nerve damage that will not recover after surgery. When diagnosed prior to atrophy, weakness or static numbness, the disease can be arrested with treatment. Mild and intermittent symptoms often resolve spontaneously.

Symptoms of CMT usually begin in early childhood or early adulthood, but can begin later. Some people do not experience symptoms until their early thirties or forties. Usually, the initial symptom is foot drop early in the course of the disease. This can also cause hammer toe, where the toes are always curled. Wasting of muscle tissue of the lower parts of the legs may give rise to a "stork leg" or "inverted champagne bottle" appearance. Weakness in the hands and forearms occurs in many people as the disease progresses.

Loss of touch sensation in the feet, ankles and legs, as well as in the hands, wrists and arms occur with various types of the disease. Early and late onset forms occur with 'on and off' painful spasmodic muscular contractions that can be disabling when the disease activates. High-arched feet (pes cavus) or flat-arched feet (pes planus) are classically associated with the disorder. Sensory and proprioceptive nerves in the hands and feet are often damaged, while unmyelinated pain nerves are left intact. Overuse of an affected hand or limb can activate symptoms including numbness, spasm, and painful cramping.

Symptoms and progression of the disease can vary. Involuntary grinding of teeth as well as squinting are prevalent and often go unnoticed by the person affected. Breathing can be affected in some; so can hearing, vision, as well as the neck and shoulder muscles. Scoliosis is common, causing hunching and loss of height. Hip sockets can be malformed. Gastrointestinal problems can be part of CMT, as can difficulty chewing, swallowing, and speaking (due to atrophy of vocal cords). A tremor can develop as muscles waste. Pregnancy has been known to exacerbate CMT, as well as severe emotional stress. Patients with CMT must avoid periods of prolonged immobility such as when recovering from a secondary injury as prolonged periods of limited mobility can drastically accelerate symptoms of CMT.

Pain due to postural changes, skeletal deformations, muscle fatigue and cramping is fairly common in people with CMT. It can be mitigated or treated by physical therapies, surgeries, and corrective or assistive devices. Analgesic medications may also be needed if other therapies do not provide relief from pain. Neuropathic pain is often a symptom of CMT, though, like other symptoms of CMT, its presence and severity varies from case to case. For some people, pain can be significant to severe and interfere with daily life activities. However, pain is not experienced by all people with CMT. When neuropathic pain is present as a symptom of CMT, it is comparable to that seen in other peripheral neuropathies, as well as postherpetic neuralgia and complex regional pain syndrome, among other diseases.

In general, ulnar neuropathy will result in symptoms in a specific anatomic distribution, affecting the little finger, the ulnar half of the ring finger, as well as the intrinsic muscles of the hand.

The specific symptoms experienced in the characteristic distribution depend on the specific location of ulnar nerve impingement. Symptoms of ulnar neuropathy may be motor, sensory, or both depending on the location of injury. Motor symptoms consistent of muscle weakness; sensory symptoms or paresthesias consist of numbness or tingling in the areas innervated by the ulnar nerve.

- Proximal impingement is associated with mixed symptoms, as the proximal nerve consists of mixed sensory and motor innervation.

- Distal impingement is associated with variable symptoms, as the ulnar nerve separates near the hand into distinct motor and sensory branches.

In cubital tunnel syndrome (a proximal impingement), sensory and motor symptoms tend to occur in a certain sequence. Initially, there may be numbness of the small and ulnar fourth finger which may be transient. If the impingement is not corrected, the numbness may become constant and progress to hand weakness. A characteristic resting hand position of "ulnar claw," where the small and ring fingers curl up, occurs late in the disease and is a sign of severe neuropathy.

By contrast, in Guyon's canal syndrome (distal impingement) motor symptoms and claw hand may be more pronounced, a phenomenon known as the ulnar paradox. Also the back of the hand will have normal sensation.

Paresthesia is an abnormal sensation such as tingling, tickling, pricking, numbness or burning of a person's skin with no apparent physical cause. The manifestation of a paresthesia may be transient or chronic, and may have any of dozens of possible underlying causes.

The most familiar kind of paresthesia is the sensation known as "pins and needles" or of a limb "falling asleep". A less well-known and uncommon but important paresthesia is formication, the sensation of bugs crawling underneath the skin.

Electroanalgesia is a form of analgesia, or pain relief, that uses electricity to ease pain. Electrical devices can be internal or external, at the site of pain (local) or delocalized throughout the whole body. It works by interfering with the electric currents of pain signals, inhibiting them from reaching the brain and inducing a response; different from traditional analgesics, such as opiates which mimic natural endorphins and NSAIDS (non-steroidal anti-inflammatory drugs) that help relieve inflammation and stop pain at the source. Electroanalgesia has a lower addictive potential and poses less health threats to the general public, but can cause serious health problems, even death, in people with other electrical devices such as pacemakers or internal hearing aids, or with heart problems.

Allodynia (Ancient Greek "" "állos" "other" and "" "odúnē" "pain") refers to central pain sensitization (increased response of neurons) following normally non-painful, often repetitive, stimulation. Allodynia can lead to the triggering of a pain response from stimuli which do not normally provoke pain. Temperature or physical stimuli can provoke allodynia, which may feel like a burning sensation, and it often occurs after injury to a site. Allodynia is different from hyperalgesia, an extreme, exaggerated reaction to a stimulus which is normally painful.

In one of the few reported cases, the subject presented with muscle weakness and fatigue, muscle twitching, excessive sweating and salivation, small joint pain, itching and weight loss. The subject also developed confusional episodes with spatial and temporal disorientation, visual and auditory hallucinations, complex behavior during sleep and progressive nocturnal insomnia associated with diurnal drowsiness. There was also severe constipation, urinary incontinence, and excessive lacrimation. When left alone, the subject would slowly lapse into a stuporous state with dreamlike episodes characterized by complex and quasi-purposeful gestures and movements (enacted dreams). Marked hyperhidrosis and excessive salivation were evident. Neurological examination disclosed diffuse muscle twitching and spontaneous and reflex myoclonus, slight muscle atrophy in the limbs, absence of tendon reflexes in the lower limbs and diffuse erythema especially on the trunk with scratching lesions of the skin.

Compulsive behaviours, stereotypies and reduplicative paramnesias can be part of the CNS spectrum.

Paresthesias of the hands, feet, legs and arms are common, transient symptoms. The briefest, electric shock type of paresthesia can be caused by tweaking the ulnar nerve near the elbow. Similar brief shocks can be experienced when any other nerve is tweaked (a tweaked neck nerve may cause a brief shock-like paresthesia toward the scalp). In the older age group, spinal column irregularities may tweak the spinal cord briefly when the head or back is turned, flexed, or extended into brief uncommon positions (Lhermitte's sign). The most common, everyday cause is temporary restriction of nerve impulses to an area of nerves, commonly caused by leaning or resting on parts of the body such as the legs (often followed by a pins and needles tingling sensation). Other causes include conditions such as hyperventilation syndrome and panic attacks. A cold sore outside the mouth (not a canker sore inside the mouth) can be preceded by tingling because a cold sore is caused by herpes simplex virus. The Varicella zoster virus (Shingles) also notably may cause recurring pain and tingling in skin or tissue along the distribution path of that nerve (most commonly in skin, along a dermatome pattern, but sometimes feeling like headache, chest or abdominal pain, or pelvic pain).

Other common examples occur when sustained pressure has been applied over a nerve, inhibiting or stimulating its function. Removing the pressure typically results in gradual relief of these paresthesias. Most pressure-induced paraesthesia results from awkward posture, such as engaging in cross-legged sitting for prolonged periods of time.

Morvan's syndrome, or Morvan's fibrillary chorea (MFC), is a rare autoimmune disease named after the nineteenth century French physician Augustin Marie Morvan. "La chorée fibrillaire" was first coined by Morvan in 1890 when describing patients with multiple, irregular contractions of the long muscles, cramping, weakness, pruritus, hyperhidrosis, insomnia, and delirium.

It normally presents with a slow insidious onset over months to years.

Approximately 90% of cases spontaneously go into remission, while the other 10% of cases lead to death.

In 1890, Morvan described a patient with myokymia (muscle twitching) associated with muscle pain, excessive sweating, and disordered sleep.

This rare disorder is characterized by severe insomnia, amounting to no less than complete lack of sleep (agrypnia) for weeks or months in a row, and associated with autonomic alterations consisting of profuse perspiration with characteristic skin miliaria (miliaria rubra, sweat rash or prickly heat), tachycardia, increased body temperature, and hypertension. Patients display a remarkable hallucinatory behavior, and peculiar motor disturbances, which Morvan reported under the term “fibrillary chorea” but which are best described in modern terms as neuromyotonic discharges.

The association of the disease with thymoma, tumour, autoimmune diseases, and autoantibodies suggests an autoimmune or paraneoplastic aetiology. Besides an immune-mediated etiology, it is also believed to occur in gold, mercury, or manganese poisoning.

Charcot–Marie–Tooth disease (CMT) is one of the hereditary motor and sensory neuropathies, a group of varied inherited disorders of the peripheral nervous system characterized by progressive loss of muscle tissue and touch sensation across various parts of the body. Currently incurable, this disease is the most commonly inherited neurological disorder, and affects approximately 1 in 2,500 people. CMT was previously classified as a subtype of muscular dystrophy.

There are different kinds or types of allodynia:

- Mechanical allodynia (also known as tactile allodynia)

- Static mechanical allodynia – pain in response when touched

- Dynamic mechanical allodynia – pain in response to stroking lightly

- Thermal (hot or cold) allodynia – pain from normally mild skin temperatures in the affected area

- Movement allodynia – pain triggered by normal movement of joints or muscles

The sciatic nerve (; also called "ischiadic nerve", "ischiatic nerve", "butt nerve") is a large nerve in humans and other animals. It begins in the lower back and runs through the buttock and down the lower limb. It is the longest and widest single nerve in the human body, going from the top of the leg to the foot on the posterior aspect. The sciatic nerve provides the connection to the nervous system for nearly the whole of the skin of the leg, the muscles of the back of the thigh, and those of the leg and foot. It is derived from spinal nerves L4 to S3. It contains fibers from both the anterior and posterior divisions of the lumbosacral plexus.

Patient feels contracture of middle and ring finger. Slight thinning of the subdigital Palm of the affected fingers. Initial pain and weakness subside with preliminary treatment with antiinflammatories, and B-complex vitamins. Initial loss of function improves almost fully.

The symptoms of MMA usually progress slowly for one to two years before reaching a plateau, and then remain stable for many years. Disability is generally slight. Rarely, the weakness progresses to the opposite limb. There is also a slowly progressive variant of MMA known as O'Sullivan-McLeod syndrome, which only affects the small muscles of the hand and forearm and has a slowly progressive course.

Electroanalgesia poses serious health problems in those patients who need other electrical equipment in their bodies, such as pacemakers and hearing aids, because the electrical signals of the multiple devices can interfere with each other and fail. People with heart problems, such as irregular heartbeat, are also at risk because the devices can throw off the normal electrical signal of the heart.

TOS affects mainly the upper limbs, with signs and symptoms manifesting in the shoulders, neck, arms and hands. Pain can be present on an intermittent or permanent basis. It can be sharp/stabbing, burning, or aching. TOS can involve only part of the hand (as in the pinky and adjacent half of the ring finger), all of the hand, or the inner aspect of the forearm and upper arm. Pain can also be in the side of the neck, the pectoral area below the clavicle, the armpit/axillary area, and the upper back (i.e., the trapezius and rhomboid area). Discoloration of the hands, one hand colder than the other hand, weakness of the hand and arm muscles, and tingling are commonly present.

TOS is often the underlying cause of refractory upper limb conditions like frozen shoulder and carpal tunnel syndrome that frequently defy standard treatment protocols. TOS can be related to Forward head posture.

A painful, swollen and blue arm, particularly when occurring after strenuous physical activity, could be the first sign of a subclavian vein compression related with an unknown TOS and complicated by thrombosis (blood clots), the so-called Paget–Schroetter syndrome or effort-induced thrombosis.

TOS can be related to cerebrovascular arterial insufficiency when affecting the subclavian artery. It also can affect the vertebral artery, in which case it could produce vision disturbances, including transient blindness, and embolic cerebral infarction.

TOS can also lead to eye problems and vision loss as a circumstance of vertebral artery compression. Although very rare, if compression of the brain stem is also involved in an individual presentation of TOS, transient blindness may occur while the head is held in certain positions.

If left untreated, TOS can lead to neurological deficits as a result of the hypoperfusion and hypometabolism of certain areas of the brain and cerebellum.

Pain caused by a compression or irritation of the sciatic nerve by a problem in the lower back is called sciatica. Common causes of sciatica include the following lower back and hip conditions: spinal disc herniation, degenerative disc disease, lumbar spinal stenosis, spondylolisthesis, and piriformis syndrome. Other acute causes of sciatica include coughing, muscular hypertension, and sneezing.