Assessing nociceptive pain and daily life interference in patients with spasticity eligible for botulinum toxin injection

Spasticity, an alteration of sensorimotor control caused by upper motor neuron lesions, manifesting as involuntary muscle activation and stretch reflex hyperactivity. Functionally, it induces muscle stiffness, limits activities of daily living, reduces mobility, and impairs quality of life[1]. Frequently accompanied by pain which triggers a maladaptive cycle characterized by muscle spasms and fatigue [2]. Botulinum toxin injection is a well-established focal treatment. A recent metanalysis suggests that it has a favorable effect on pain, besides reducing muscle tone. While its analgesic properties are primarily studied in neuropathic pain, the nociceptive component of spasticity-related pain strongly supports its clinical use. Mechanistically, reducing muscle hyperactivity decreases pathological stretch, joint overload, and subsequent tissue nociceptive activation. At the moment, the characterization of this nociceptive pain component remains lacking. This study aims to identify the presence of nociceptive pain, analyzing its severity and interference with daily life in a cohort of neurological patients eligible for botulinum toxin treatment. Demographic, anthropometric and topographical data were collected from patients candidate for botulinum toxin treatment. Functional independence was evaluated using the Functional Independence Measure (FIM), while pain via the Brief Pain Inventory, divided into the Severity Index (BPI-SI) and the Interference Index (BPI-II). Continuous variables were expressed as mean and standard deviation, and categorical variables as frequencies and percentages. Mean pain severity and interference scores were compared across the different disease cohorts. Correlation analyses were performed between pain, anthropometric data, and functional autonomy within the entire cohort and inside each pathological subgroup. We included 53 patients (mean age:34.70±19.21years and body mass index:23.87±5.52), with BPI-SI mean score of 2.07±2.38, and BPI-II score of 2.26±3.01. Pain interference correlated significantly with advancing age (r=0.490;p=0.002) and increasing BMI (r=0.337;p=0.041). No statistically significant differences emerged for anthropometric data, BPI-SI, and FIM (p>0.05) among the disease subgroups. Conversely, pain interference was markedly higher in patients with stroke outcomes compared to those with Cerebral Palsy (CP) (mean ranks:13.50vs8.50;p=0.030). A similar trend, though non-significant, was observed in patients with Multiple Sclerosis (MS) compared to CP (p=0.065), whereas no substantial difference was found between stroke and MS (p=0.550). Patients candidate for botulinum toxin treatment present with pain levels and disability that are independent of topography and primary diagnosis. However, the interference of the nociceptive component on daily life is influenced by bio-clinical factors and exhibits distinct profiles depending on the underlying pathology. The lower impact observed in CP suggests a potential chronic-congenital adaptation mechanism to the symptom, is absent in adult-onset pathologies where pain imposes a significantly more disabling burden. These phenotypic determinants offer important predictive indicators to optimize both therapeutic and rehabilitative targeting.