Objective assessment of gait after intrathecal baclofen in hereditary spastic paraplegia

Abstract

Sirs: Sporadic spastic paraplegia (SSP) and hereditary spastic paraplegia (HSP) are heterogeneous neurodegenerative disorders. On physical examination spasticity of the lower limbs is often predominant, whereas paraparesis may be mild [1, 2]. The gait disorder of SSP/HSP patients which is the cardinal source of disability in these patients has been recently characterized [3]. The treatment of spastic paraplegia is symptomatic and limited to oral antispastic drugs and physiotherapy. In 1984 Penn [4] showed that intrathecal baclofen (ITB) could alleviate spinal cord spasticity. The efficacy of ITB on spasticity has been proven in several studies [5, 6]. In these studies ITB was used as a symptomatic treatment to reduce painful spasm and muscle contractions in mostly wheelchair bound patients. However, SSP/HSP patients are often able to walk even in advanced stages of their disease. Therefore, ITB therapy in SSP/HSP has the special requirement of reducing spasticity but preserving gait function. So far most clinical trials on spasticity rely on rating scales such as the modified “Ashworth Scale of Spasticity” (ASH), which may not adequately reflect the functional benefit in gait in SSP/HSP patients. In the particular case of ITB therapy for SSP/HSP the indication for an ITB pump implantation should moreover be based on the global clinical impression of gait improvement after an ITB test injection. Unfortunately, there are no scientific operational data to test the functional benefit of ITB in SSP/HSP. Here we describe the clinical effect of ITB in 10 patients, who were all treated with oral antispastic drugs and ongoing physiotherapy. Additionally we tested the usefulness of a three-dimensional movement analysis system for the selection of candidates for an ITB pump implantation. The gait of 10 SSP/HSP patients before and after a testing dose of 25 or 50 μg ITB was examined with this method, which is described elsewhere in detail [7]. In cooperation with the responsible physiotherapists we clinically distinguished responders (group 1; n = 5) from non responders (group 2; n = 5) based on the global clinical impression of gait improvement after ITB. Group 1 was recommended for an ITB pump implantation, whereas group 2 was not. With respect to spastic tone SSP/HSP patients showed a significant reduction of the ASH after ITB (p = 0.014). These result are comparable to the study of Penn et al. who analysed the effect of ITB via an implanted pump system [6]. We found an increased gait velocity accompanied by larger step length and a reduced step width after ITB in all patients, but no significant change in other kinematic gait parameters at a self chosen comfortable speed. Additionally, gait analysis was also performed with a fixed velocity of 1 km/h to eliminate the variable influence of speed. Under this condition group 1 presented an increased range of motion (ROM) of the ankle angle. Furthermore group 1 showed a reduction of the minimum knee angle as shown in a patient in Fig. 1. Gait parameters alone, however, did not allow us to separate clinical responders and non responders. An ITB pump implantation was performed in three of the five screened patients of group 1. Two patients did not opt for ITB owing to subjective unsteadiness and weakness in the lower extremities. We were able to collect follow up gait analysis data of two patients under chronic ITB. Both patients showed an effect of chronic ITB (mean dosage 60 μg/day), which was equivalent to the effect of the test bolus (Fig. 2). In conclusion, our findings show that ITB is a potential treatment option in SSP/HSP. However, only 50 % of our patients were recommended for a pump implantation. Therefore it can be assumed that all patients showed a variable effect of ITB that was probably too strong and a formerly existing weakness was unmasked by the ITB in some patients. In the quantitative gait analysis an improvement of gait was documented in the gait velocity and the step length. However, gait analysis alone was not able to discriminate between clinical responders and non-responders. This may be due to the relatively small number of investigated patients. If so, in the individual patient the clinical examination of gait before and after bolus injection of ITB in a multidisciplinary assessment by a neurologist and physiotherapists experienced with gait disorders is decisive and cannot be replaced by a technical assessment alone.