Science //

A phantom menace

For many amputees ongoing pain is part of everyday life, writes Alex Gillis.

Imagine waking up every day in pain. It started after minor surgery to your leg, and appears to have no cause. Your doctor is flummoxed and your friends think it’s all in your head. This is a dire reality for many sufferers of chronic pain.While chronic pain has a huge array of potential causes, perhaps the most perplexing is neuropathic – resulting from nervous system damage. We’re really not sure how it happens, and there is a complete paucity of treatments. Household analgesics like aspirin have no effect – only opioids will consistently take the pain away.

The most widely known example is phantom limb pain – more than half of those who have undergone some amputation report some form of this. This reality is not apparent in the feel-good human-interest stories of those who have lost limbs. Public consciousness consists of a rose-tinted view of athletes breaking records at the Paralympics or trekking up mountains.The concept of a phantom limb, the apparent presence of the removed tissue, is startling in itself – pain in that non-existent extremity is truly distressing. A deep-seated conflict between what is consciously known and what is subconsciously felt reflects the brain’s struggle to adapt. Showing people overcoming the loss of a limb to achieve remarkable things is uplifting, but presents a skewed view. There is much more than simply missing that extremity, not least of which is the possibility of daily pain in a foot that isn’t even there.

The continued apparent presence of a limb is a good avenue to understanding chronic pain from nerve damage. The confusion of signals that occurs is very similar to that in amputation – and may produce the same result. Our nerves are surprisingly vulnerable to damage – some forms of the herpes virus, chemotherapy drugs, and even routine surgeries present a significant risk of chronic pain. Research into chronic pain has generally employed animal models – while inducing human suffering is considered unconscionable, we think it ethically permissible to cause animals pain. There is an immediate contradiction here. If we are to assume that non-humans are sufficiently different to us such that we may ethically cause them ongoing pain, how could they possibly inform us about the human condition? Conversely, if a lab rat does experience pain like we do, how can we subject them to it? Suggesting rodents experience true pain rather than a pain-like state invariably leads to accusations of anthropomorphism, but conversely it’s possible we’ve erroneously convinced ourselves that the human experience is unique.

We tend to think of pain as a sense, a mechanism for conveying information. This overlooks a critical component, and that is pain as an experience. Pain is overwhelming, focusing our attention on solely the hurt and how to end it. The concept of it being “all in your head” is self-defeating – all pain is experienced in your brain. Our belief that pain follows injury hampers our ability to empathise with those whose condition, by definition, is pain without injury.

While many mechanisms have been proposed – from aberrant nerve firing to sensitising of the brain to inputs – none have satisfactorily explained the vagaries of these syndromes. Perhaps most confronting is that despite decades of research there has been no real improvement in treatment, as the vast majority of pain patients see vast impacts on their quality of life. Dismissing chronic pain as merely imaginary or ‘mental’ further sidelines these patients. Our lack of progress demonstrates the need for a new approach.