Parsonage Turner syndrome (PTS) is characterized by the sudden onset of shoulder and upper arm pain followed by progressive (worsening over time) weakness and/or atrophy of the affected area. The pain is felt along the path of one or more nerves and often has no obvious physical cause. The network of nerves involved in this syndrome is called the brachial plexus and it controls movement and sensation in the shoulders and arms. The cause is still unknown (idiopathic). However, researchers believe that most cases are due to an autoimmune response following exposure to an illness or environmental factor. Suspected triggers include viral and bacterial infections, surgery, vaccinations, injury, childbirth, strenuous exercise, certain medical procedures, and various health conditions. Treatment is symptomatic and may include pain relievers, corticosteroids and physical therapy.

PTS is one of two forms of neuralgic amyotrophy. The other form is hereditary and is caused by mutations in the SEPT9 gene in about 85% of cases.

• Infections (both viral and bacterial)
• Surgery
• Vaccinations
• Childbirth
• Certain medical procedures, such as a spinal tap or imaging studies that require administration of radiologic dye
• Strenuous exercise
• Certain medical conditions, including connective tissue disorders and autoimmune disorders
• Injury

Some researchers believe that Parsonage Turner syndrome is a multifactorial condition, which means that it is caused by an interaction between environmental and genetic factors. In this case, a person may have a genetic susceptibility to PTS due to one or more genes, but won't develop the condition unless they are exposed to certain environmental triggers (such as one or more of those listed above).

Parsonage Turner syndrome, also known as idiopathic neuralgic amyotrophy, is not inherited. However, there is an inherited form of neuralgic amyotrophy called hereditary neuralgic amyotrophy. This form is inherited in an autosomal dominant manner.

In some cases, nerves and muscles outside of the shoulder and upper arm region are affected, such as the lumbosacral plexus (causing symptoms in the legs) or phrenic nerve (affecting the diaphragm).

A diagnosis of Parsonage Turner syndrome often is suspected based on the presence of characteristic signs and symptoms. Specialized tests may be recommended to further investigate the shoulder pain and/or muscle weakness, and to rule out other conditions that can cause similar features. These tests may include nerve conduction studies (tests that determine the ability of a specific nerve to relay a message to the brain), electromyography, magnetic resonance imaging (MRI scan), and/or an X-ray.

Pain medications may be prescribed depending on the severity of the nerve pain. After the acute phase, different medications known as co-analgesics may be administered. These include gabapentin, carbamazepine, and amitryptiline. These drugs specifically treat nerve pain. Other techniques for pain management include application of heat or cold, and transcutaneous electrical nerve stimulation (a method of pain relief in which a special device transmits low-voltage electrical impulses through electrodes on the skin to an area of the body that is in pain).

Many people with PTS have physical therapy and/or occupational therapy to maintain muscle strength and range of motion once the pain begins to subside. Surgeries such as nerve grafting or tendon transfer to restore movement and function to the shoulder muscles and joint may be considered if other treatment options are not effective.

The long-term outlook (prognosis) for people with Parsonage Turner syndrome varies. Some people may experience only a single episode of pain, and fully recover the strength and functionality of their shoulder. Others may have multiple episodes throughout their lives. It has been reported that approximately 80% of people recover within 2 years of the start of symptoms, and approximately 90% recover within 3 years. Traditionally, it was believed that most people would recover around 70-90% of their original strength and function level. However, more recent research suggests that long-term complications are more common than previously thought. People with bilateral (affecting both sides of the body) involvement or multiple episodes are more likely to have a poorer prognosis.