1Royal Devon and Exeter Healthcare Trust, Rheumatology, Exeter EX2 5DW, 2Royal National Hospital for Rheumatic Diseases in conjunction with The Department of Medical Sciences, University of Bath, Bath BA1 1RL and 3Cardiff University, School of Psychology, Cardiff CF10 3YG, UK
Correspondence to: R. C. Haigh. E-mail: richard.haigh{at}rdehc-tr.swest.nhs.uk
We thank Helliwell for his considered arguments. Our premise was that central nervous system changes governed the subjective experience of stiffness in a limb even after it is amputated, and in support of the hypothesis, maintain that current evidence fails to confirm a consistent relationship between objective and subjective measures of joint stiffness.
Indeed, local treatments of inflammation, such as aspiration and injection of corticosteroid into a joint, have a number of consequences in addition to a local anti-inflammatory effect that may influence both peripheral and central nervous systems, resulting in altered sensory feedback and a modified motor output. In addition, our subject reported a reduction in stiffness in the joints in her intact limb as well as her phantom limb following systemic steroid therapy. Thus, it is difficult to accept that peripheral mechanisms alone generate and perpetuate stiffness. Furthermore, distal sensory function may not be normal in rheumatoid arthritis at all [1], despite biothesiometer vibration perception thresholds being normal in the cited study [2].
We agree that semantics, terminology and understanding of the concept(s) of stiffness can complicate the issue and Helliwell suggests that our subjects may have found it difficult to differentiate between pain and stiffness, particularly on waking. However, in addition to the diurnal sensations our subjects experienced, we specifically enquired about the impact of movement on their phantom joints. Whereas the pain of an arthritic joint is commonly exacerbated by exercise, stiffness is usually relieved. Our subjects all reported that exercise relieved their perceived stiffness and that it returned to pre-exercise levels on rest.
Finally, we reiterate our proposal that perceived joint stiffness may be determined by impairment to central brain processes, although related to the initial peripheral rheumatoid disease process.
The authors have declared no conflicts of interest.
References