Peripheral nerve injuries can be classified in two different ways. Neurotmesis is classified under the Seddon system which is defined by three grades of nerve injury. The mildest grade is referred to as neurapraxia and is characterized by a reduction or complete blockage of conduction across a segment of nerve while axonal continuity is maintained and nerve conduction is preserved. These injuries are almost always reversed and a recovery takes place within days or weeks. The second classification of the Seddon system is referred to as axonotmesis which is a more severe case of peripheral nerve injury. Axonotmesis is classified by an interruption of the axons, but a preservation of the surrounding connective tissues around the axon. These injuries can heal themselves at about 1mm/day, therefore resulting in recovery to be possible but at a slower rate than neurapraxia. The last and most severe case of peripheral nerve injury is known as neurotmesis, which in most cases cannot be completely recovered from even with surgical repair.

The second classification of nerve injury is known as the Sunderland classification which is more complex and specific. This classification uses five different degrees of nerve injury, the first one being the least severe and the equivalent to neurapraxia and the most severe being the fifth degree and having the same classification as neurotmesis. The second through fourth degrees are dependent on the variance of axon discontinuity and are classified under Seddon’s classification of axonotmesis.

Axillary nerve palsy patients present themselves with differing symptoms. For instance, some axillary nerve palsy patients complain that they cannot bend their arm at the elbow, however no other pain or discomfort exists. To further complicate diagnosis, onset of palsy can be delayed and may not be noticed until 12-24 hours after the trauma of shoulder region occurred. Therefore it is important to recognize the symptoms, but also to realize that different people have various combinations of them.

Symptoms include:

- cannot bend arm at the elbow

- deficiency of deltoid muscle function

- different regions of skin around the deltoid area can lack sensation

- unable to raise arm at the shoulder

Symptoms of neurotmesis include but are not limited to pain, dysesthesias (uncomfortable sensations), and complete loss of sensory and motor function of the affected nerve.

This is the least severe form of nerve injury, with complete recovery. In this case, the axon remains intact, but there is myelin damage causing an interruption in conduction of the impulse down the nerve fiber. Most commonly, this involves compression of the nerve or disruption to the blood supply (ischemia). There is a temporary loss of function which is reversible within hours to months of the injury (the average is 6–9 weeks). Wallerian degeneration does not occur, so recovery does not involve actual regeneration. There is frequently greater involvement of motor than sensory function with autonomic function being retained. In electrodiagnostic testing with nerve conduction studies, there is a normal compound motor action potential amplitude distal to the lesion at day 10, and this indicates a diagnosis of mild neuropraxia instead of axonotmesis or neurotmesis.

A variety of nerve types can be subjected to neurapraxia and therefore symptoms of the injury range in degree and intensity. Common symptoms of neurapraxia are disturbances in sensation, weakness of muscle, vasomotor and sudomotor paralysis in the region of the affected nerve or nerves, and abnormal sensitivity of the nerve at the point of injury. It has been observed that subjective sensory symptoms include numbness, tingling, and burning sensations at the site of the injury. Objective sensory symptoms are generally minimal in regards to touch, pain, heat, and cold. In cases of motor neuron neurapraxia, symptoms consist of flaccid paralysis of the muscles innervated by the injured nerve or nerves.

Symptoms are often transient and only last for a short period of time immediately following the injury. However, in severe cases of neurapraxia, symptoms can persist for weeks or months at a time.

Anyone experiencing radial nerve dysfunction could also experience any of the following symptoms:

- Lost ability or discomfort in extending the elbow

- Lost ability or discomfort bending hand back at the wrist

- Numbness

- Abnormal sensations near the thumb, index and middle fingers

- Sharp or burning pain

- Weakness in grip

- Drooping of the hand, also called wrist drop

A nerve contains sensory fibers, motor fibers, or both. Sensory fibers lesions cause the sensory problems below to the site of injury. Motor fibers injuries may involve lower motor neurons, sympathetic fibers, and or both.

Assessment items include:

- Sensory fibers that send sensory information to the central nervous system.

- Motor fibers that allow movement of skeletal muscle.

- Sympathetic fibers that innervate the skin and blood vessels of the four extremities.

In assessment, sensory-motor defects may be mild, moderate, or severe. Damage to motor fibers results in paralysis of the muscles. Nervous plexus injuries create more signs and symptoms from sensory-motor problems (such as brachial plexus injuries). In these cases, the prognosis depends on the amount of damage and the degree of functional impairment.

Nerve injury is injury to nervous tissue. There is no single classification system that can describe all the many variations of nerve injury. In 1941, Seddon introduced a classification of nerve injuries based on three main types of nerve fiber injury and whether there is continuity of the nerve. Usually, however, (peripheral) nerve injury is classified in five stages, based on the extent of damage to both the nerve and the surrounding connective tissue, since supporting glial cells may be involved. Unlike in the central nervous system, neuroregeneration in the peripheral nervous system is possible. The processes that occur in peripheral regeneration can be divided into the following major events: Wallerian degeneration, axon regeneration/growth, and nerve reinnervation. The events that occur in peripheral regeneration occur with respect to the axis of the nerve injury. The proximal stump refers to the end of the injured neuron that is still attached to the neuron cell body; it is the part that regenerates. The distal stump refers to the end of the injured neuron that is still attached to the end of the axon; it is the part of the neuron that will degenerate but that remains in the area toward which the regenerating axon grows. The study of peripheral nerve injury began during the American Civil War and has greatly expanded to the point of using growth-promoting molecules.

Symptoms (and signs) of radial neuropathy vary depending on the severity of the trauma; however, common symptoms may include wrist drop, numbness (back of the hand and wrist), and inability to voluntarily straighten the fingers. Loss of wrist extension is due to loss of the ability to move of the posterior compartment of forearm muscles.

In the event of lacerations to the wrist area the symptom would therefore be "sensory". Additionally, depending on the type of trauma other nerves may be affected such as the median nerve and axillary nerves.

Axonotmesis is an injury to the peripheral nerve of one of the extremities of the body. The axons and their myelin sheath are damaged in this kind of injury, but the endoneurium, perineurium and epineurium remain intact. Motor and sensory functions distal to the point of injury are completely lost over time leading to Wallerian Degeneration due to ischemia, or loss of blood supply. Axonotmesis is usually the result of a more severe crush or contusion than neurapraxia.

Axonotmesis mainly follows a stretch injury. These stretch injuries can either dislocate joins or fracture a limb, due to which peripheral nerves are severed. If the sharp pain from the exposed axon of the nerve is not observed, one can identify a nerve injury from abnormal sensations in their limb. A doctor may ask for a Nerve Conduction Velocity (NCV) test to completely diagnose the issue. If diagnosed as nerve injury, Electromyography performed after 3 to 4 weeks shows signs of denervations and fibrillations, or irregular connections and contractions of muscles.

Neurapraxia is a disorder of the peripheral nervous system in which there is a temporary loss of motor and sensory function due to blockage of nerve conduction, usually lasting an average of six to eight weeks before full recovery. Neurapraxia is derived from the word apraxia, meaning “loss or impairment of the ability to execute complex coordinated movements without muscular or sensory impairment”.

This condition is typically caused by a blunt neural injury due to external blows or shock-like injuries to muscle fibers and skeletal nerve fibers, which leads to repeated or prolonged pressure buildup on the nerve. As a result of this pressure, ischemia occurs, a neural lesion results, and the human body naturally responds with edema extending in all directions from the source of the pressure. This lesion causes a complete or partial action potential conduction block over a segment of a nerve fiber and thus a reduction or loss of function in parts of the neural connection downstream from the lesion, leading to muscle weakness.

Neurapraxia results in temporary damage to the myelin sheath but leaves the nerve intact and is an impermanent condition; thus, Wallerian degeneration does not occur in neurapraxia. In order for the condition to be considered neurapraxia, according to the Seddon classification system of peripheral nerve injury, there must be a complete and relatively rapid recovery of motor and sensory function once nerve conduction has been restored; otherwise, the injury would be classified as axonotmesis or neurotmesis. Thus, neurapraxia is the mildest classification of peripheral nerve injury.

Neurapraxia is very common in professional athletes, especially American football players, and is a condition that can and should be treated by a physician.

Radial neuropathy (or radial mononeuropathy) is a type of mononeuropathy which results from acute trauma to the radial nerve that extends the length of the arm. It is known as transient paresthesia when sensation is temporarily abnormal.

Axillary nerve palsy is a neurological condition in which the axillary (also called circumflex) nerve has been damaged by shoulder dislocation. It can cause weak deltoid and sensory loss below the shoulder. Since this is a problem with just one nerve, it is a type of Peripheral neuropathy called mononeuropathy. Of all brachial plexus injuries, axillary nerve palsy represents only .3% to 6% of them.

Facial nerve paralysis is characterised by unilateral facial weakness, with other symptoms including loss of taste, , and decreased salivation and tear secretion. Other signs may be linked to the cause of the paralysis, such as s in the ear, which may occur if the facial palsy is due to shingles. Symptoms may develop over several hours. Acute facial pain radiating from the ear may precede the onset of other symptoms.

A tumor compressing the facial nerve anywhere along its complex pathway can result in facial paralysis. Common culprits are facial neuromas, congenital cholesteatomas, hemangiomas, acoustic neuromas, parotid gland neoplasms, or metastases of other tumours.

Often, since facial neoplasms have such an intimate relationship with the facial nerve, removing tumors in this region becomes perplexing as the physician is unsure how to manage the tumor without causing even more palsy. Typically, benign tumors should be removed in a fashion that preserves the facial nerve, while malignant tumors should always be resected along with large areas of tissue around them, including the facial nerve. While this will inevitably lead to heightened paralysis, safe removal of a malignant neoplasm is worth the often treatable palsy that follows. In the best case scenario, paralysis can be corrected with techniques including hypoglossal-facial nerve anastomosis, end-to-end nerve repair, cross facial nerve grafting, or muscle transfer/transposition techniques, such as the gracilis free muscle transfer.

Patients with facial nerve paralysis resulting from tumours usually present with a progressive, twitching paralysis, other neurological signs, or a recurrent Bell's palsy-type presentation.

The latter should always be suspicious, as Bell's palsy should not recur. A chronically discharging ear must be treated as a cholesteatoma until proven otherwise; hence, there must be immediate surgical exploration. Computed tomography (CT) or magnetic resonance (MR) imaging should be used to identify the location of the tumour, and it should be managed accordingly.

Other neoplastic causes include leptomeningeal carcinomatosis.

Radial nerve dysfunction is also known as radial neuropathy or radial mononeuropathy. It is a problem associated with the radial nerve resulting from injury consisting of acute trauma to the radial nerve. The damage has sensory consequences, as it interferes with the radial nerve's innervation of the skin of the posterior forearm, lateral three digits, and the dorsal surface of the side of the palm. The damage also has motor consequences, as it interferes with the radial nerve's innervation of the muscles associated with the extension at the elbow, wrist, and figers, as well the supination of the forearm. This type of injury can be difficult to localize, but relatively common, as many ordinary occurrences can lead to the injury and resulting mononeuropathy. One out of every ten patients suffering from radial nerve dysfunction do so because of a fractured humerus.

Based on the location of the nerve damage, brachial plexus injuries can affect part of or the entire arm. For example, musculocutaneous nerve damage weakens elbow flexors, median nerve damage causes proximal forearm pain, and paralysis of the ulnar nerve causes weak grip and finger numbness. In some cases, these injuries can cause total and irreversible paralysis. In less severe cases, these injuries limit use of these limbs and cause pain.

The cardinal signs of brachial plexus injury then, are weakness in the arm, diminished reflexes, and corresponding sensory deficits.

1. Erb's palsy. "The position of the limb, under such conditions, is characteristic: the arm hangs by the side and is rotated medially; the forearm is extended and pronated. The arm cannot be raised from the side; all power of flexion of the elbow is lost, as is also supination of the forearm".

2. In Klumpke's paralysis, a form of paralysis involving the muscles of the forearm and hand, a characteristic sign is the "clawed hand", due to loss of function of the ulnar nerve and the intrinsic muscles of the hand it supplies.

Signs and symptoms may include a limp or paralyzed arm, lack of muscle control in the arm, hand, or wrist, and lack of feeling or sensation in the arm or hand. Although several mechanisms account for brachial plexus injuries, the most common is nerve compression or stretch. Infants, in particular, may suffer brachial plexus injuries during delivery and these present with typical patterns of weakness, depending on which portion of the brachial plexus is involved. The most severe form of injury is nerve root avulsion, which usually accompanies high-velocity impacts that commonly occur during motor-vehicle collisions or bicycle accidents.

In terms of the signs/symptoms of ulnar neuropathy trauma and pressure to the arm and wrist, especially the elbow, the medial side of the wrist, and other sites close to the course of the ulnar nerve are of interest in this condition..Many people complain of sensory changes in the fourth and fifth digits. Rarely, an individual actually notices that the unusual sensations are mainly in the medial side of the ring finger (fourth digit). Sometimes the third digit is also involved, especially on the ulnar (medial) side. The sensory changes can be a feeling of numbness or a tingling, pain rarely occurs in the hand. Complaints of pain tend to be more common in the arm, up to and including the elbow area, which is probably the most common site of pain in an ulnar neuropathy.

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.

Crutch paralysis is a form of paralysis which can occur when either the radial nerve or part of the brachial plexus, containing various nerves that innervate sense and motor function to the arm and hand, is under constant pressure, such as by the use of a crutch. This can lead to paralysis of the muscles innervated by the compressed nerve. Generally, crutches that are not adjusted to the correct height can cause the radial nerve to be constantly pushed against the humerus. This can cause any muscle that is innervated by the radial nerve to become partially or fully paralyzed. An example of this is wrist drop, in which the fingers, hand, or wrist is chronically in a flexed position because the radial nerve cannot innervate the extensor muscles due to paralysis. This condition, like other injuries from compressed nerves, normally improves quickly through therapy.

In a pure lesion of the anterior interosseous nerve there may be weakness of the long flexor muscle of the thumb (Flexor pollicis longus), the deep flexor muscles of the index and middle fingers (Flexor digitorum profundus I & II), and the pronator quadratus muscle.

There is little sensory deficit since the anterior interosseous nerve has no cutaneous branch.

Most patients experience poorly localised pain in the forearm. The pain is sometimes referred into the cubital fossa and elbow pain has been reported as being a primary complaint.⁠

The characteristic impairment of the pincer movement of the thumb and index finger is most striking.

Ulnar neuropathy is a disorder involving the ulnar nerve. Ulnar neuropathy may be caused by entrapment of the ulnar nerve with resultant numbness and tingling. Motor function can be assessed by testing for a positive Froment's sign, or making an OK sign (which the individual will be unable to do), little finger abduction can be tested as well.

Symptoms of ulnar neuropathy or neuritis do not necessarily indicate an actual physical impingement of the nerve; indeed, any injury to the ulnar nerve may result in identical symptoms. In addition, other functional disturbances may result in irritation to the nerve and are not true "impingement". For example, anterior dislocation and "snapping" of ulnar nerve across the medial epicondyle of the elbow joint can result in ulnar neuropathy.

Entrapment of other major sensory nerves of the upper extremities result in deficits in other patterns of distribution. Entrapment of the median nerve causes carpal tunnel syndrome, which is characterized by numbness in the thumb, index, middle, and half of the ring finger. Compression of the radial nerve causes numbness of the back of the hand and thumb, and is much more rare.

A simple way of differentiating between significant median and ulnar nerve injury is by testing for weakness in flexing and extending certain fingers of the hand. Median nerve injuries are associated with difficulty flexing the index and middle finger when attempting to make a fist. However, with an ulnar nerve lesion, the pinky and ring finger cannot be "unflexed" when attempting to extend the fingers.

Some people are affected by multiple nerve compressions, which can complicate diagnosis.