General Types of PNS Disorders

Anesthesia is the loss of sensation (esthesis means sensation). It may be a pathological condition if it happens spontaneously, or it may be induced to facilitate surgery or some other medical treatment.

Hyperesthesia is an abnormal acuteness to sensation--an increased sensitivity.

Paresthesia is an abnormal spontaneous sensation such as tingling, prickling, or burning.

Neuralgia consists of severe spasms of throbbing or stabbing pain along the pathway of a nerve. Two types of neuralgia are described below.

Trigeminal neuralgia, also called tic douloureux, involves one or more of the trigeminal nerve branches and consists of sharp bursts of pain in the face. This disorder often has a trigger point in or around the mouth which, when touched, elicits the pain response in some other part of the face. The cause of trigeminal neuralgia is unknown.

Ischiadica (is'ke-ad'i-ka), or sciatica, is a neuralgia of the ischiadic nerve, with pain radiating down the back of the thigh and leg. The most common cause is a herniated lumbar disk, resulting in pressure on the spinal nerves contributing to the lumbar plexus. Ischiadica may also be produced by ischiadic neuritis arising from number of causes, including mechanical stretching during exertion, vitamin deficiency, or metabolic disorders (such as gout or diabetes).

Neuritis is a general term referring to inflammation of a nerve that has a wide variety of causes, including mechanical injury or pressure, viral or bacterial infection, poisoning by drugs or other chemicals, and vitamin deficiencies. Neuritis in sensory nerves is characterized by neuralgia or may result in anesthesia and loss of reflexes in the affected area. Neuritis in motor nerves results in loss of motor function.

Facial palsy (or Bell's palsy ) is a unilateral paralysis of the facial muscles. The affected side of the face droops because of the absence of muscle tone. Facial palsy involves the facial nerve and may result from facial nerve neuritis.

Infections

Herpes is a family of diseases characterized by skin lesions, which are caused by a group of closely related viruses. The term is derived from the Greek work herpo meaning to creep and indicates a spreading skin eruption. The viruses apparently reside in the ganglia of sensory nerves and case lesions along the course of the nerve.

Herpes simplex I is usually characterized by one or more lesions on the lips or nose. The virus apparently resides in the trigeminal ganglion. Eruptions are usually recurrent and often occur in times of reduced resistance such as during a cold episode. For this reason they are called cold sores or fever blisters. A different herpes virus, herpes simplex II, or genital herpes, is usually responsible for a sexually transmitted disease causing lesions on the external genitalia.

The varicella virus causes chickenpox in children and shingles in older adults, a disease called herpes zoster. Normally, this virus first enters the body in childhood to cause chickenpox. The virus then lies dormant in the spinal ganglia for many years and can become active during a time of reduced resistance to cause shingles, a unilateral patch of skin blisters and discoloration along the path of one or more spinal nerves, most commonly around the waist. The symptoms may persist for 3 to 6 months.

Poliomyelitis ("polio" or infantile paralysis; the term polio means gray matter) is a disease caused by Poliovirus hominis. It is actually a CNS infection, but its major effect is on the peripheral nerves and the muscles they supply. The virus infects the motor neurons in the anterior horn of the central gray matter of the spinal cord. The infection causes degeneration of the motor neurons, which results in paralysis and atrophy of the muscles innervated by those nerves.

Anesthetic leprosy is a bacterial infection of the peripheral nerves caused by Mycobacterium leprae. The infection results in anesthesia, paralysis, ulceration, and gangrene.

Genetic and Autoimmune Disorders

Myotonic dystrophy is an autosomal dominant hereditary disease characterized by muscle weakness, dysfunction, and atrophy and by visual impairment as a result of nerve degeneration.

Myasthenia gravis is an autoimmune disorder resulting in a reduction in the number of functional acetylcholine receptors in neuromuscular junctions. T-cells of the immune system break down acetylcholine receptor proteins into two fragments, which trigger antibody production by the immune system. Myasthenia gravis results in fatigue and progressive muscular weakness because of the neuromuscular dysfunction.

Neurofibromatosis is a genetic disorder in which small skin lesions appear in early childhood followed by the development of multiple subcutaneous neurofibromas, which are benign tumors resulting from neurolemmocyte (Schwann cell) proliferation. The neurofibromas may slowly increase in size and number over several years and cause extreme disfiguration. The most famous patient afflicted with this disorder was the so-called Elephant Man.