Does a hormone we produce naturally hold the key to stopping chronic back pain?
Recent research at Johns Hopkins University School of Medicine in the US seems to indicate so, offering the possibility of a new treatment for the condition.
The study on mice, published in the Journal of Bone Research, suggested a treatment using parathyroid hormone (PTH) could tackle many types of back pain at their biological root cause. PTH is a hormone produced by the parathyroid glands – four pea-sized glands in the neck.
The hormone helps control calcium levels in the blood, typically by increasing its absorption from the gut and kidneys.
It also affects bone metabolism: the hormone can strengthen and build bone – although excessive levels can cause bone weakness or loss.
For years, synthetic, manmade PTH has been used to treat hypoparathyroidism, when the body doesn’t produce enough PTH, as well as to treat osteoporosis, the bone-thinning condition that affects more than three million people in Britain.
Anecdotally, a significant number of patients taking synthetic PTH for these conditions also reported an added benefit – their back pain got better. Until now, the reason why has been a mystery.
For the latest study, scientists injected mice daily with PTH for up to two months – while examining their spinal tissue using high-resolution imaging and measuring their movement and response to pressure.
Back pain has many causes, including injury, congenital disorders such as scoliosis (curvature of the spine), arthritis and lifestyle factors
The researchers found that the PTH-treated mice had denser, more stable vertebral endplates – these are the thin layers of bone and cartilage that separate spinal discs from vertebrae. These mice also showed less sensitivity to pain, tolerated pressure better and were more active.
As well as strengthening bone density, PTH was found to physically push away nerves from damaged spinal areas by stimulating osteoblasts, bone-building cells, to release a protein, Slit3, which repels them.
As Dr Janet Crane, the research lead, explained: when the spine degenerates, ‘pain-sensing nerves grow into regions where they normally do not exist. Our findings show parathyroid hormone can reverse this process by activating natural signals that push these nerves away’.
This means PTH effectively ‘rewires’ pain signals at source, permanently reversing the biological causes of chronic back pain, rather than just temporarily reducing or blocking pain signals as we do with, for example, anti-inflammatory drugs or painkillers.
‘This is an exciting discovery,’ says Bob Chatterjee, a consultant spinal surgeon at The London Clinic. ‘It is a definite cause for optimism. This builds on things that we already knew. PTH is not a cure-all for everything but in certain situations it is promising.’
Back pain has many causes, including injury; congenital disorders such as scoliosis (curvature of the spine); arthritis; and lifestyle factors, such as being too sedentary (sitting for long periods puts excess pressure on your spinal discs and reduces core strength), smoking (which can restrict blood flow and alter posture) or obesity (which may also alter posture and put pressure on the spine).
Mr Chatterjee says: ‘This paper is looking at structural back pain, meaning the degeneration of structures such as discs and joints.
‘Sometimes, this can be part of the ageing process or due to abnormal stresses on the spine from, for example, poor posture or injury.
‘Reports suggest up to 40 per cent of patients suffer from structural back pain and the majority are aged over 50.
‘So, if your back pain is coming from degeneration within the vertebral endplates, there’s good evidence PTH can help by strengthening bone while repelling nerves from sensitive regions where they wouldn’t normally be.
‘Equally, if your symptoms are coming from the facet joints [small joints between vertebra] there’s also a chance PTH treatment will help because when the facet joints become damaged or arthritic (or any joint does) it promotes the growth of these abnormal nerve endings.’
But it’s likely to be less effective at treating back pain that’s due to muscle or ligament damage (whiplash, for example) or lifestyle factors.
In addition, possible side-effects of PTH treatment could include sending ‘your calcium metabolism in the wrong direction’, suggests Mr Chatterjee.
He explains: ‘Calcium is an important ingredient in nerve signalling and function. If you get a decrease in blood calcium then that can often cause nerve hyper-excitability, typically causing symptoms such as numbness, tingling and muscle cramps.
‘In contrast, if you have too much calcium released into the blood it can lead to fatigue, brain fog, sleep disturbance, even irritability and depression.’
Current back pain solutions revolve around non-medical techniques such as physiotherapy, osteopathy and acupuncture; or medications such as painkillers, anti-inflammatories and steroid injections – or, as a last resort, surgery.
‘The problem is,’ says Mr Chatterjee, ‘they are not really treating the problem at source – we are treating the effects of the problem rather than the root cause.
‘The PTH therapy, in theory, would be treating the root cause.’
