Effectiveness of intramuscular injections of botulinum toxin in the treatment of disabling cerebellar tremor of the hand

Abstract

Hypermetric tremors, i.e. of cerebellar origin (essential tremor, cerebellar stroke or tumor, multiple sclerosis, hereditary spinocerebellar ataxias), directly relate to iterative hypermetria by delayed antagonist correction at each movement and cause significant functional and social difficulties. Botulinum toxin injections (BoNT) can reduce the amplitude of any tremor, but at the expense of muscle weakening when the injection is performed on both agonists and antagonists contributing to tremor. We measured the functional effects one month after botulinum toxin injections into agonist muscles only (eg pronator injection sparing supinators) in patients with cerebellar tremor causing upper limb disability. We retrospectively analyzed data from two volumetric tests (30-second and 5-table-to-mouth tests) in 14 patients (age 67 ± 19 years) with upper limb cerebellar tremor before and one month after their last BoNT injection into selected agonist muscles. The tests consisted of measuring the amount of remaining water (in mm) in a polystyrene cup (90 mm height), maintained a full to the brim initially, after 30 seconds of holding the cup with the arm outstretched (V30) and after 5 table-to-mouth back and forth movements (VX5). Injections were well tolerated based on an open-ended questioning. The amounts of water remaining in the cup with V30 and VX5 tests were: pre BoNT injection V30 = 40.9 ± 8.8 mm and VX5 = 25.2 ± 8.5 mm; 1 month post injection V30 = 61.4 ± 7.47 mm (+49%; p = 0.08, t -test pre vs. post) and VX5 = 47.4 ± 8.7 mm (+47%; P = 0.07). The improvements of nearly 50% in volumetric tests after injection suggests functional efficiency on upper limb cerebellar tremor of injecting botulinum toxin into one agonist only. Explorations of correlations with tremor electromyographic parameters and patient subjective impression about daily hand use in real life will be the subject of a future analysis.