Impaired sensorimotor control of the hand in congenital absence of functional muscle spindles
Smith LJ[1], Palma J-A[2], Norcliffe-Kaufmann L[2] , Kaufmann H[1, 2] and Macefield VG[1,3,4]
1. School of Medicine, Western Sydney University, Sydney, Australia
2. Dysautonomia Center, Department of Neurology, New York University School of Medicine, New York, USA
3. Baker Heart & Diabetes Institute, Melbourne, Australia
4. NeuRA (Neuroscience Research Australia), Sydney, Australia
Patients with Hereditary Sensory & Autonomic Neuropathy type III (HSAN III) exhibit marked gait disturbances. The cause of the gait ataxia is not known, but we recently showed that functional muscle spindle afferents in the leg, recorded via intraneural microelectrodes inserted into the peroneal nerve, are absent in HSAN III, although large-diameter cutaneous afferents are intact (1). Moreover, there is a tight correlation between loss of proprioceptive acuity at the knee and the severity of gait impairment (2). Here we tested the hypothesis that manual motor performance is also compromised in HSAN III, attributed to the predicted absence of muscle spindles in the intrinsic muscles of the hand. Manual performance in the Purdue pegboard task was assessed in 12 individuals with HSAN III and 12 age-matched healthy controls. The mean (+/-SD) pegboard score (number of pins inserted in 30 s) was 8.1+/-1.9 and 8.6+/-1.8 for the left and right hand respectively, significantly lower than the scores for the controls (14.3+/-2.9 and 15.5+/-2.0; p<0.0001). In five patients we inserted a tungsten microelectrode into the ulnar nerve at the wrist. No spontaneous or stretch-evoked muscle afferent activity could be identified in any of the 11 fascicles supplying intrinsic muscles of the hand, whereas rich tactile afferent activity could be recorded from 4 cutaneous fascicles. We conclude that functional muscle spindles are absent in the hand, and likely absent in the long finger flexors and extensors, and that this largely accounts for the poor manual motor performance in HSAN III.
1. Macefield VG, Norcliffe-Kaufmann L, Gutiérrez J, Axelrod, F & Kaufmann H. (2011) Brain 134: 3198-3208
2. Macefield VG, Norcliffe-Kaufmann LJ, Axelrod F & Kaufmann H (2013) Movement Disorders 28: 823-827