Phantom sensation and phantom pain commonly co-exist. Phantom sensation occurs in most amputees, and is experienced as resembling the pre-amputation limb in shape and size and may include feelings of posture and movement. Patients may describe feelings of warmth, cold, itching, tingling or electric sensations. Phantom sensation usually appears soon after amputation and can last from weeks to years, but is not experienced as being painful.
Some patients also describe the phenomenon of ‘telescoping’. This is where the distal part of the phantom limb is felt to be closer to the stump or within the stump itself. For example, forearm amputees may describe feeling that their amputated hand is attached to their elbow stump. This probably occurs because the cortical magnification of the hand is proportionally over represented on the somatosensory cortex.
Around 60 – 80% of amputees will experience phantom pain in the early post-operative period with the incidence decreasing with time following amputation. The incidence of phantom limb pain appears to be independent of age, gender and level or side of amputation. 75% of patients will develop phantom pain within the first few days after amputation but the first emergence of phantom pain may be delayed and develop several years later. Phantom pain is often regarded as a chronic pain problem lasting for many years following amputation. Several studies, however, have shown a reduction in pain over periods of 2 – 5 years post amputation, although most continue to experience some pain beyond this.
A number of factors have been shown to be predictive of the onset of phantom limb pain post-operatively. Patients found to be most at risk are those who have severe pain in the amputated limb pre-operatively, patients undergoing bilateral amputation and patients with persisting stump pain. The incidence of phantom limb pain is however lower in paediatric amputees and very rare in those with congenitally absent limbs.
Phantom pain is most commonly thought of as occurring following amputation of a limb but it is also well recognised following amputation of other bodily parts including testis, penis, breast, eye or tongue. The incidence of phantom pain following mastectomy is quoted as high as 15% but is a poorly recognised and seldom acknowledged sequelae of this type of operation.
Phantom pain is usually felt as being located in the distal part of the amputated limb and is often described as being gripping, burning, shooting or cramping in character. Unlike many forms of neuropathic pain, phantom limb pain is commonly intermittent although some patients will experience constant pain. Once established, phantom limb pain can be very resistant to treatment; for instance dense regional anaesthetic blockade provides only limited benefit. Indeed, a number of cases have been reported of patients developing phantom limb pain for the first time while under spinal anaesthetic and also of patients experiencing exacerbations of pre-existing phantom pain with spinal and epidural anaesthesia. This reinforces the view that phantom limb pain is not solely a phenomenon of the peripheral nervous system but involves more widespread and complicated central processes.
Stump pain is common in the early post-operative period. This is an acute nociceptive pain that usually resolves as the wound heals. Stump pain may persist in 5 – 10% of patients due to on-going local pathology or an acute neuropathic process. Sensory examination of the stump at this time may demonstrate hyperalgesia and allodynia. Surgical revision should be avoided if at all possible and is only indicated for localised pathology such as osteomyelitis or abscess. Persistent stump pain may be a risk factor for phantom pain.
At a later stage, once the patient begins rehabilitation and mobilisation, stump pain may develop or be exacerbated due to a poorly fitting prosthesis.