Muscle Characteristics in Pediatric Hereditary Spastic Paraplegia vs. Bilateral Spastic Cerebral Palsy: An Exploratory Study

Abstract

Hereditary spastic paraplegia (HSP) is a neurological, genetic disorder that predominantly presents with lower limb spasticity and muscle weakness. Pediatric pure HSP types with infancy or childhood symptom onset resemble in clinical presentation to children with bilateral spastic cerebral palsy (SCP). Hence, treatment approaches in these patient groups are analogous. Altered muscle characteristics, including reduced medial gastrocnemius (MG) muscle growth and hyperreflexia have been quantified in children with SCP, using 3D-freehand ultrasound (3DfUS) and instrumented assessments of hyperreflexia, respectively. However, these muscle data have not yet been studied in children with HSP. Therefore, we aimed to explore these MG muscle characteristics in HSP and to test the hypothesis that these data differ from those of children with SCP and typically developing (TD) children. A total of 41 children were retrospectively enrolled including (1) nine children with HSP (ages of 9-17 years with gross motor function levels I and II), (2) 17 age-and severity-matched SCP children, and (3) 15 age-matched typically developing children (TD). Clinically, children with HSP showed significantly increased presence and severity of ankle clonus compared with SCP (p = 0.009). Compared with TD, both HSP and SCP had significantly smaller MG muscle volume normalized to body mass (p ≤ 0.001). Hyperreflexia did not significantly differ between the HSP and SCP group. In addition to the observed pathological muscle activity for both the low-velocity and the change in high-velocity and low-velocity stretches in the two groups, children with HSP tended to present higher muscle activity in response to increased stretch velocity compared with those with SCP. This exploratory study is the first to reveal MG muscle volume deficits in children with HSP. Moreover, high-velocity-dependent hyperreflexia and ankle clonus is observed in children with HSP. Instrumented impairment assessments suggested similar altered MG muscle characteristics in pure HSP type with pediatric onset compared to bilateral SCP. This finding needs to be confirmed in larger sample sizes. Hence, the study results might indicate analogous treatment approaches in these two patient groups.

Keywords: cerebral palsy; hereditary spastic paraplegia; hyperreflexia; instrumented impairment assessments; muscle morphology; muscle volume; spasticity; ultrasound.

Figure 1

Flowchart of the patient selection process for the children with hereditary spastic paraplegia (HSP). N, number.

Figure 2

Example illustration of (A) ankle joint angle vs. time graph, (B) ankle angular velocity vs. time graph, (C) root-mean square-electromyography (RMS-EMG) vs. time graph, and (D) 3D bar graph of average normalized RMS-EMG across three position zones and the two velocities of the medial gastrocnemius (MG) muscle, in a child with hereditary spastic paraplegia (HSP) and an age-matched child with spastic cerebral palsy (SCP) (20). Graphs (A–C) presented both a slow (dashed line) and high (continuous line) velocity stretch, whereby 0 s represent the time at the maximal velocity. In addition, the RMS-EMG vs. time graph (C) for the child with HSP indicates a clear ankle clonus, with 24 oscillations over a time period of 4 s. For the SCP case, this graph (C) indicates a catch during the high velocity stretch. In graph (D), the position zones indicate 10–90% of range of motion (ROM) divided in three equal parts. Velocity 1 and velocity 2 represent the low-velocity and high-velocity muscle stretches, respectively. High-velocity-dependent activation patterns are presented in both the HSP and SCP case.