Cervical injuries of the spinal cord frequently lead to hypertonia characterized by disabling spasticity and dystonia involving the upper and lower limb. Spasticity has been defined by Lance (1980) as “a velocity exaggerated increase in the tonic stretch reflexes (muscle tone) resulting from hyperactivity of the stretch reflex.” More recently, the EU-SPASM Thematic Network or Consortium (Support Network for the Assembly of Database for Spasticity Measurement) presented an updated definition of spasticity that reflects current research findings and clinical interpretations. Spasticity has been re-defined as “disordered sensorimotor control, resulting from an upper motor neurone lesion, presenting as intermittent or sustained involuntary activation of muscles” (Pandyan et al., 2005).
The management of severe cases of hypertonia can be challenging as it can be refractory to oral medications. Many studies have shown that intrathecal delivery of baclofen has been effective for refractory hypertonia in the lower extremity. Baclofen, 4-amino-3 (p-chlorophenyl) butyric acid works by binding to the inhibitory presynaptic GABA-B receptors in the spinal cord (Meythaler et al., 1999). Intrathecal delivery of the drug facilitates achievement of therapeutic levels in the cerebral spinal fluid (CSF) while minimizing systemic side effects (drowsiness, confusion). Burns and Meythaler (2001) is the only study published which deals with hypertonia involving the upper extremity post-SCI. Further discussion regarding the management of hypertonia can be found in the spasticity chapter.
Burns and Meythaler (2001) showed a statistically significant decrease in Ashworth and reflex scores in upper extremity hypertonia due to pathology at the level of the spinal cord. However, this is the only study published to date regarding intrathecal baclofen use in a SCI population.
There is level 4 evidence (from one case series study: Burns & Meythaler 2001) that intrathecal baclofen may be an effective treatment for upper extremity hypertonia of spinal cord origin.