Joint stiffness in a phantom limb: evidence of central nervous system involvement in rheumatoid arthritis.

OBJECTIVE: The nature and cause of perceived joint stiffness (PJS), a well-established and defining symptom of rheumatoid arthritis (RA), remains unclear. We hypothesized that changes in the central nervous system (CNS) may determine and maintain this subjective experience of stiffness in a limb even after it is amputated. To test this hypothesis, patients with a phantom limb (PL) who had experienced characteristic RA stiffness prior to amputation were systematically investigated.
METHODS: Three patients with a current diagnosis of RA and lower limb amputation were investigated to determine the nature and pattern of pain and stiffness in their PL and intact limb. In addition to standard physical examination, pain and stiffness severity was measured using visual analogue scales for both limbs. The duration and timing of stiffness were also recorded for each limb.
RESULTS: In all three cases, the pattern of perceived RA stiffness was similar for the intact limb and the PL. All three patients described stiffness in their PL which mirrored that of physical RA joint symptoms in terms of quality, frequency, diurnal variation, location, distribution and response to medication [non-steroidal anti-inflammatory drug (NSAID), corticosteroid, opiate and disease-modifying anti-rheumatic drug (DMARD)]. Unilateral exercise (or attempted exercise) relieved stiffness only in the limb being exercised.
CONCLUSION: The extent to which the subjective experience of perceived stiffness could be dissociated from the assumed original peripheral source was strikingly illustrated in RA patients with phantom limbs. We suggest that the PJS characteristic of RA is generated and maintained by secondary plastic changes in the CNS, although causally related to the initial peripheral rheumatoid disease process.