Causalgia is technically known as complex regional pain syndrome type II (CRPS II). It’s a neurological disorder that can produce long-lasting, intense pain.

CRPS II arises after an injury or trauma to a peripheral nerve. Peripheral nerves run from your spine and brain to your extremities. The most common site of CRPS II pain is in what’s called the “brachial plexus.” This is the bunch of nerves that run from your neck to your arm. CRPS II is rare, affecting slightly fewer than 1 person out of 100,000.

Unlike CRPS I (formerly known as reflexive sympathetic dystrophy), CRPS II pain is generally localized to the area around the injured nerve. If the injury occurred to a nerve in your leg, for example, then pain settles in your leg. Conversely, with CRPS I, which doesn’t involve an apparent nerve injury, pain from a hurt finger can radiate throughout your body.

CRPS II can occur wherever there’s a peripheral nerve injury. Peripheral nerves run from your spine to your extremities, which means CRPS II is usually found in your:

  • arms
  • legs
  • hands
  • feet

Regardless of what peripheral nerve is injured, symptoms of CRPS II tend to remain the same and include:

  • burning, aching, excruciating pain that lasts six months or longer and seems disproportionate to the injury that brought it on
  • pins and needles sensation
  • hypersensitivity around the area of injury, in which being touched or even wearing clothes can trigger sensitivity
  • swelling or stiffness of the affected limb
  • abnormal sweating around the injured site
  • skin color or temperature changes around the injured area, such as skin that looks pale and feels cold and then red and warm and back again

At the root of CRPS II is peripheral nerve injury. That injury can result from a fracture, sprain, or surgery. In fact, according to one investigation, 1.8 percent of nearly 400 elective foot and ankle surgery patients developed CRPS II after surgery. Other causes of CRPS II include:

However, it’s still unknown why some people respond so dramatically to these events and others don’t.

It’s possible that people with CRPS (either I or II) have abnormalities in the linings of their nerve fibers, making them hypersensitive to pain signals. These abnormalities can also initiate an inflammatory response and induce changes to blood vessels. This is why so many people with CRPS II can have swelling and skin discoloration at the site of the injury.

There is no one test that can definitively diagnose CRPS II. Your doctor will perform a physical exam, record your medical history, and then order tests that may include:

  • an X-ray to check for broken bones and loss of bone minerals
  • an MRI to look at soft tissues
  • thermography to test skin temperature and blood flow between injured and noninjured limbs

Once other more common conditions such as fibromyalgia are eliminated, your doctor can make a CRPS II diagnosis more confidently.

CRPS II treatment generally consists of medications and certain types of physical and nerve-stimulating therapies.

If over-the-counter pain relievers like acetaminophen (Tylenol) or ibuprofen (Advil) aren’t providing relief, your doctor may prescribe stronger drugs. These can include:

  • steroids to reduce inflammation
  • certain antidepressants and anticonvulsants, such as Neurontin, that have pain-relieving effects
  • nerve blocks, which involve injecting an anesthetic directly into the affected nerve
  • opioids and pumps that inject drugs directly into your spine to block pain signals from nerves

Physical therapy, used to sustain or improve range of motion in painful limbs, is also often used. Your physical therapist may also try what’s called transcutaneous electrical nerve stimulation (TENS), which sends electrical impulses through fibers in your body to block pain signals. In research studying people with CRPS I, those receiving TENS therapy reported more pain relief than those not receiving it. Battery-operated TENS machines are available for at-home use.

Some people have found that heat therapy — using a heating pad periodically throughout the day — can also help. Here’s how you can make your own heating pad.

Whenever you experience prolonged pain that interferes with your life and isn’t relieved by over-the-counter medications, you should see your doctor.

CRPS II is a complex syndrome that may need a variety of specialists to treat it. These specialists may include experts in orthopedics, pain management, and even psychiatry, as chronic pain can take a toll on your mental health.

While CRPS II is a serious condition, there are effective treatments. The sooner it’s diagnosed and treated, the better your chances are for a positive outcome.