SINOPSIS

Objective: a critical review of the literature on the clinical effects of phenol nerve and muscle blocks and the duration of effects for the treatment of local spasticity. Mapping out the advantages and disadvantages of phenol sets the stage for newly developed methods like radiofrequency thermocoagulation and botulinum toxin. Study selection: a computer search was carried out (MEDLINE) for the period 1966 to 1994 using the key words: spasticity, nerve block, motor point block, neurolysis, peripheral denervation, and phenol. In addition, references given in any relevant publications were examined and recent volume numbers of relevant, nonindexed journals were screened. Articles in English, French, German, or Dutch were included. Randomized and nonrandomized clinical trials as well as case series were selected if: (1) patients were treated for spasticity of the extremities, and (2) the treatment consisted of peripheral nerve or muscle blocks by phenol. Data synthesis: Forty-five studies were reviewed. For each study a success percentage could be calculated. Case studies reported the highest success percentages (71%), followed by the uncontrolled (61%), and nonrandomized controlled studies (45%). Percutaneous nerve blocks seem somewhat more effective than muscle blocks, with a success percentage of 66% when compared with 61%. So-called 'open nerve' blocks seem less effective (54%). In nine studies the effects of 110 phenol blocks in the upper extremity were reported, whereas 8 studies with 260 patients/blocks presented the results of phenol injections into the lower extremity. Treatment of spasticity of the lower extremity seems more effective than treating the upper extremity, with an overall success rate of 89% vs. 59%.
For the duration of phenol block response, a median was calculated, based on the longest duration of effects reported in the 45 studies. The effects of nerve blocks (13 studies) are reported to last longer than muscle blocks (6 studies): a median of 22 months vs. 11.5 months. The effects in the lower extremity studies (6) reportedly last longer than those in the upper extremity studies (6): a median of 14.5 and 9.5 months, respectively. Neither for the nerve blocks nor for the muscle blocks could a dose-response relation be demonstrated. Moreover, no relation was found between dose and duration of effects.
The most severe complication of percutaneous nerve blocks is painful paraesthesia, occurring in 11% of the patients. The main complications of muscle blocks were transient tenderness and swelling at the multiple injection sites, whereas surgical or open nerve blocks are complicated by wound infections.
Conclusions: There are some indications that phenol injections might reduce spasticity, although the duration of effects is limited. However, this conclusion is based on subjective, clinical impressions of treatment effects. Blinded, unprejudiced, and objective assessments of the effects of phenol are still lacking. Furthermore, distortion of the presented results by placebo effects could not be excluded. Although phenol blocks are already widely used in clinical practice, placebo-controlled efficacy studies, assessed according to present research rules, are needed to prove the real value of phenol. Well-designed randomized clinical trials might also clarify the effectiveness of peripheral nerve and muscle blocks by phenol when compared with other recently developed treatments.