Why ice cream gives you those blinding headaches
. . . and an infected tooth can give you earache. It’s all down to the brain mixing up messages
WAKING up with a sore shoulder is often down to an awkward sleeping position or overdoing it at the gym, and can be easily fixed with a new pillow or a few stretches.
But sometimes pain in your shoulder is actually a sign of something else — potentially more serious and seemingly unrelated to that particular part of the body — such as gallstones, stomach ulcers or liver damage.
This is due to a phenomenon known as referred pain, where the unpleasant sensation is felt at a site that’s distant from the underlying cause.
It’s the same reason why pain down the left arm can be a sign of a heart attack and why we get ice-cream headaches, where extreme cold experienced in the throat and palate causes pain that’s felt in the head.
Referred pain is thought to be the result of the brain mixing up messages from various nerves all around the body.
This is known as the ‘convergence theory’, which is that nerves coming from different parts of the body converge in the spinal cord, the super highway that funnels everything to the brain, and this can lead to crossed lines and messages getting mixed up.
So, for example, during a heart attack, sensations enter the spinal cord at the same level as sensations coming from the left arm or shoulder. This makes the brain think the pain is actually coming from the arm or shoulder.
Overloaded with messages, the brain interprets nerve signals as coming from tissues that are more prone to feeling pain, such as the skin or muscles, rather than organs such as the gut, heart or kidneys (known as visceral pain).
This is because the skin is densely packed with nerve cells and our brain frequently gets messages from them, such as when we touch something.
‘Because the nerves of the heart and other internal organs are rarely activated, and those from the skin much more so, the brain seems to interpret organ signals as coming from the skin,’ says Dr Michael Platt, a consultant in anaesthetics at Imperial College Healthcare NHS Trust.
‘Everyone has referred pain at some time. It is down to the nervous system and its development in the embryo.’
There are various points along the spinal cord where different signals meet — for example, nerves from the stomach convey pain signals to the same area as the skin between the shoulder blades — which is why pain originating in one particular part of the body may typically be felt in another.
In most cases, doctors can only identify the source of pain by a process of elimination of other more obvious possibilities.
Types of referred pain are still being discovered and could lead to new treatments.
Here, we reveal the most common types of pain and where they could be coming from.
EARACHE? MAYBE A DENTIST CAN HELP
IT’S well known that heart attacks can affect the left arm, but one of the first symptoms can also be pain in the teeth and jaw. The chest pain of angina can also be felt here.
A study in 2009 in the Journal of Applied Oral Science suggested that doctors could distinguish between genuine toothache and referred pain in the tooth by injecting local anaesthetic into the gum.
This would block nerves in the tooth from sending signals. If pain persists then doctors can assume it’s being referred to the tooth, rather than a dental problem.
On the other hand, some earache may not actually be due to a problem in the ear, but the result of an infected tooth. That’s because the same nerve that carries signals from the ear also carries them from the jaw — it means you wouldn’t get relief from your earache until the tooth is treated.
Pain in the jaw may also be a sign of endometriosis, where tissue that behaves like the lining of the womb is found outside the womb, according to researchers at Florida State University.
SHOULDERING PAIN OF STOMACH ULCER
APART from the more obvious causes, such as arthritis or injury, there are a number of conditions that can result in a sore arm or shoulder. For example, pain in the right shoulder may be a symptom of problems with the gall bladder, which is tucked under the right rib cage.
Shoulder pain more generally can also be linked to liver diseases and appendicitis, as well as shingles and ovarian cysts.
Meanwhile, pain in the shoulders, neck and armpit can also be signs of pneumonia, where there is inflammation in the lungs.
And recently, doctors at the University of Michigan described how a 42-year- old woman who complained of pain in her right shoulder was found to have a stomach ulcer.
They say the shoulder pain was down to gastric juices irritating the diaphragm, which is linked to the nerves that supply the shoulder.
One of the best known examples of referred pain is in the left arm due to a heart attack.
Nerves from damaged heart tissue send pain signals to the brain, which converge in the spinal cord with signals from the left side of the chest and arm.
However, in women, pain from the heart is usually felt right across both shoulders, indicating that there are also gender differences in the patterns of referred pain.
TRY A NECK RUB FOR A HEADACHE
ICE-CREAM headache — a shortlived, but very intense pain in the forehead — is a common example of referred pain that comes from the back of the throat.
It’s thought the rapid cooling and rewarming of the capillaries (tiny blood vessels) cause the nerves to transmit signals to the brain.
These get mixed with messages coming from other nerves and the brain interprets them as coming from the forehead.
And the excruciating pain we associate with a migraine is in some cases the result of neck problems. This is known as a cervicogenic headache, thought to be caused by a muscular problem in the neck.
This means that physiotherapy of the neck may be effective for some headaches, say researchers at Murdoch University, Australia.
Meanwhile, neck pain may be referred from illnesses in the lungs and diaphragm.
WHEN BACK PAIN IS TUMMY TROUBLE
MOST of us will experience back pain at some point. While sometimes this is triggered by bad posture or a problem in the spine, it could have underlying causes as diverse as problems with the pancreas, lungs, heart and stomach. These may affect different parts of the back.
For example, lower back pain may be due to a prolapsed bladder, kidney problems or pancreatitis.
A study of 38,000 women at Queensland University found that women with gastrointestinal issues were up to three times more likely to suffer lower back pain.
Pain at the top of the spine may be coming from the heart or oesophagus, while pain in the middle of the back could be coming from stomach problems.
Meanwhile, back pain such as sciatica, which results from damaged discs, may be referred and felt in the legs. That’s because a damaged disc can put pressure on nerves that supply the legs so the pain is felt there and may even be referred to the stomach and toes.
CAN SPICY FOOD BE BAD FOR BLADDERS?
RESEARCHERS at Northwestern University in the U.S. have found that flare-ups of pelvic pain, which are usually put down to bladder problems, may actually be due to spicy food irritating the colon, a theory they dubbed the ‘pepperoni pizza hypothesis’.
Their study in the journal Nature Clinical Practice Urology showed that the nerves from the bladder and colon go into the same area of the spinal cord, near the tailbone.
And while people with pelvic pain are usually treated with antibiotics, as they are thought to have a bladder infection, they may actually benefit from painkillers. Meanwhile, pain felt in the testicles may be due to pain originating from the centre of the back.
This is because the testicles migrate downwards from the same area when an embryo develops, but the associated nerves remain at the same level. And pain in the penis may be coming from a problem in the bladder or urethra.