Elbow proprioception is normal in patients with a congenital absence of functional muscle spindles

Key points: Individuals with hereditary sensory and autonomic neuropathy type III (HSAN III), also known as Riley–Day syndrome or familial dysautonomia, do not have functional muscle spindle afferents but do have essentially normal cutaneous mechanoreceptors. Lack of muscle spindle feedback from the legs may account for the poor proprioception at the knee and the ataxic gait typical of HSAN III. Given that functional muscle spindle afferents are also absent in the upper limb, we assessed whether proprioception at the elbow was likewise compromised. Passive joint angle matching showed that proprioception was normal at the elbow, suggesting that individuals with HSAN III rely more on cutaneous afferents around the elbow. Abstract: Hereditary sensory and autonomic neuropathy type III (HSAN III) is a rare neurological condition that features a marked ataxic gait that progressively worsens over time. We have shown that functional muscle spindle afferents are absent in the upper and lower limbs in HSAN III, and we have argued that this may account for the ataxia. We recently used passive joint angle matching to demonstrate that proprioception of the knee joint is very poor in HSAN III but can be improved towards normal by application of elastic kinesiology tape across the knee joints, which we attribute to the presence of intact cutaneous mechanoreceptors. Here we assessed whether proprioception was equally compromised at the elbow joint, and whether it could be improved through taping. Proprioception at the elbow joint was assessed using passive joint angle matching in 12 HSAN III patients and 12 age-matched controls. There was no difference in absolute error, gradient or correlation coefficient of the relationship between joint angles of the reference and indicator arms. Unlike at the knee, taping did not improve elbow proprioception in either group. Clearly, the lack of muscle spindles compromised proprioception at the knee but not at the elbow, and we suggest that the HSAN III patients rely more on proprioceptive signals from the skin around the elbow.