Complex regional pain syndrome

The fracture has healed, the cast is off and the X-ray looks fine, yet the hand hurts so much that it cannot be touched. The skin swings between red and hot and cold and bluish, the fingers are swollen and stiff, and the sleeve of a T-shirt causes genuine pain. This is not a matter of having a low pain threshold: in some people the nervous system does not return to its usual settings after an injury, and the pain starts living a life of its own, separate from the damage that started it. The condition is called complex regional pain syndrome. It is uncommon, it is often recognised late, and almost everything that decides the outcome happens in the first few months.

Why the pain outgrows the injury

It usually begins with an injury: a fracture, a sprain, a heavy blow, a cut, a burn, an operation. Sometimes it is enough for the limb to have spent a few weeks immobilised in a cast. In most people everything heals as expected; in a few, after days or weeks, the pain not only fails to settle but spreads well beyond the site of the injury, so that a hurt finger ends up as pain across the whole hand and forearm.

Why this happens to those particular people is not known. It looks less like one broken part than like several systems misfiring at once: the nerves of the limb pass on signals differently, the small blood vessels and sweat glands change how they work, local inflammation switches on, and in the brain the internal map of where the limb is and how big it is becomes distorted. In most of those affected no damage to any specific nerve can be found; less often the syndrome follows a confirmed nerve injury, and both versions are treated the same way. It is not regarded as an inherited disease, it affects people of any age including children, and it is more common in women.

What happens to the arm or leg

The main feature is pain out of all proportion to the injury and to the time that has passed. People describe burning, shooting pains and a deep ache, mixed with tingling and numbness; usually one limb is affected.

A distinctive feature is a distorted sensitivity of the skin. The touch of a bedsheet, the jet of a shower or a draught can hurt, although none of it should; doctors call this allodynia. Alongside it comes hyperalgesia, in which something that ought merely to be uncomfortable is felt as severe pain. Flare-ups last from a few days to several weeks and are triggered by stress, cold, poor sleep and sudden increases in activity.

Besides pain, other changes appear in the limb:

• the skin shifts in colour and temperature, at times red, hot and dry, at other times cold, pale or bluish and clammy; on brown and black skin the colour change is harder to see, so go by the difference in temperature compared with the healthy side;
• swelling develops, the joints stiffen and movement becomes steadily harder;
• hair and nails grow either too fast or too slowly, and the nails turn brittle and ridged;
• tremor, twitching and spasms appear, and sometimes the fingers lock into an abnormal position;
• the limb feels foreign, larger or smaller than the healthy one;
• sleep is disturbed, and not only because of the pain.

In neglected cases, where the arm or leg has gone unused for years, it can end in wasted muscle, permanently shortened tendons and skin sores that will not close.

What must be ruled out without delay

A swollen, hot, painful limb after an injury is not only this syndrome. Several conditions look similar but need attention within hours, and they are exactly the ones that get missed when everything is put down to pain that is simply dragging on.

Seek urgent care the same day if:

• pain under a cast or dressing builds quickly, feels like pressure from inside and flares sharply when you try to straighten the fingers, and those fingers are cold, pale or numb: the dressing has to come off straight away;
• the whole calf or thigh swells and warms, the skin feels tight and there is tenderness along a vein, which is how a deep vein thrombosis shows itself, particularly after a cast, an operation or a long spell of immobility;
• breathlessness, chest pain on breathing in, a racing heart or coughing up blood are added to the swelling: call the emergency services;
• a fever and chills start, redness spreads with a sharp edge, pus comes from a wound or red streaks appear;
• a joint is hot, tensely swollen and cannot be moved even slightly;
• the limb is visibly deformed, an area of skin has lost sensation, or movement has gone completely.

Without emergency urgency but also without putting it off, see a doctor if constant pain is stopping you doing ordinary things and has lasted longer than you would expect from that injury. Waiting to see whether it settles on its own is the commonest reason people lose the chance of a quick recovery.

How the diagnosis is reached

There is no single test or scan that confirms the syndrome. The diagnosis rests on a combination of findings, and not a haphazard one: an agreed international list groups them into four headings, namely sensation, skin colour and temperature, swelling and sweating, and movement and the appearance of the limb. Both what the patient reports and what the doctor finds by hand are taken into account, and the examination has to be gentle so as not to set off a flare lasting days.

Tests are ordered to exclude other causes: blood tests, X-rays, a scan if needed, an ultrasound of the veins and nerve conduction studies. Normal results here do not mean nothing is wrong; they mean precisely that what has been found is not some other disease. After that a pain specialist is needed, and the referral is worth asking for early, because rehabilitation programmes work better the sooner they start.

Movement is the backbone of treatment, however odd that sounds

The first instinct is to shield the limb and let nobody near it. That is exactly what makes things worse: an immobilised arm swells more, the joints harden, the skin grows even more sensitive and the muscles waste. The aim is the opposite, to bring the limb back into daily life gradually without provoking flares that last for days.

• Ordinary use. Leaning on it, picking things up, dressing with the affected hand, a little every day and as far as it is tolerated.
• Supervised exercise. From simple stretches to pool work and light weights. It matters that the physiotherapist understands this condition: too forceful a programme increases both pain and swelling.
• Desensitisation. The skin is touched with fabrics of different texture, cotton wool, silk, wool, a towel. You start on the healthy side, remember the sensation, then transfer it to the affected side. The first weeks are unpleasant, after which sensitivity evens out.
• Work on the body image. Telling left from right, imagining movements, and exercises in front of a mirror that reflects the healthy hand.
• Pacing, sleep and relaxation. A little every day rather than everything on a good day and nothing on a bad one; breathing techniques and a settled sleep pattern reduce flares, because stress is one of their main triggers.

Medicines: what to expect from them

No drug removes this syndrome. Medicines are there to bring the pain down far enough for rehabilitation to become possible. Hence the rule: if a drug has produced no effect within a few weeks, it is stopped rather than pushed to the highest dose.

• Ordinary painkillers and anti-inflammatories help with the pain of the injury itself and of overworked neighbouring muscles, but do little for pain of nerve origin.
• Anticonvulsants have proved useful for nerve pain quite apart from epilepsy. Common effects are drowsiness, dizziness and weight gain; in the first weeks there may be a small increase in the risk of low mood and suicidal thoughts. They must not be stopped abruptly and are withdrawn gradually.
• Tricyclic antidepressants are prescribed here not for depression but against nerve pain; they also improve sleep, which is why they are taken in the evening. They can cause a dry mouth, blurred vision, constipation, palpitations and difficulty passing urine. They too are tapered off.
• Topical preparations containing local anaesthetics or capsaicin act only on their patch of skin and are easier to tolerate than tablets.
• Opioids work poorly for this kind of pain and do considerable harm: nausea, constipation, mental fogginess and, with long use, lowered sex hormones and dependence. They are kept for short courses under specialist supervision.
• Nerve blocks and drugs acting on bone turnover are sometimes used early on, always on the decision of a specialist centre.

If the pain stays severe despite six months of a programme followed honestly, spinal cord stimulation is discussed: a small generator is placed under the skin and a thin electrode is led to the spinal cord, so that weak impulses alter how pain is perceived. A trial is done first with the electrodes alone, and only if the relief is clear is the whole system implanted.

Mood and sleep: part of the illness, not a weakness of character

Living with constant pain is hard, and anxiety and low mood here are the rule rather than the exception. This is not a separate nuisance: low mood wrecks sleep, drains the will to do the exercises and rehabilitation grinds to a halt, so the psychological side is dealt with on equal terms with the physical one. Cognitive behavioural therapy helps, not by persuading anyone that the pain is imaginary but by unpicking how thoughts, fear of movement and behaviour feed one another; it is often run in small groups alongside the rehabilitation sessions.

If thoughts of harming yourself or ending your life appear, ask for help the same day, from your doctor, an urgent mental health service or the emergency services. This is not a situation in which to wait for a scheduled appointment.

How it changes over time

The outlook is better than it seems at the height of the illness: in most people the pain and the visible changes gradually recede over the first year or two and the limb goes back to work, though not always fully. In a minority the pain lasts for years, and there is as yet no way of telling in advance who will be in that group. What certainly does matter is how long it takes to start treatment and whether the person keeps moving.

A flare after exertion, a cold or a difficult week does not mean everything is back to square one: it is a temporary setback after which you return to your previous level of exercise rather than abandoning it, and what works worst is a pause lasting months. If the pain changes character, a new symptom appears or the changes spread to the other limb, that is a reason to be seen again rather than to file everything under the diagnosis you already have.

Online consultation

A remote appointment is well suited to exactly the things people tend to postpone. The doctor will ask how recovery from the injury went, match the character of the pain against the timeline, ask to see both limbs on camera, explain which tests are needed to exclude other causes and which specialist to be referred to. Online is also the sensible place to discuss how well the medicines are tolerated, how to come off them, the plan for returning to activity and what to do during a flare. The urgent signs in the list above are not assessed through a screen: with those, go to a doctor in person or call the emergency services.

This material is for information only and does not replace medical advice.