Dynamics of upper limb spastic paresis post stroke: Mechanisms, measurement and treatment

Upper limb motor impairments are one of the most common impairments post stroke and occur in up to 80% of all patients. Motor impairments post stroke comprise negative and positive upper motor neuron features. The negative features involve deficit symptoms, such as loss of voluntary motor function, i.e. paresis, and the positive features encompass involuntary muscle overactivity. The combination of negative and positive features leads to the typical clinical presentation of spastic paresis, which shows a considerable, still unexplained, variability between patients and changes over time post stroke. Clinically, spastic paresis is characterized by a loss of motor function, increased resistance to passive joint movement (i.e. joint hyper-resistance), reduced passive range of motion and postural change. Spasticity is an important topic in stroke rehabilitation and is considered to be one of the forms of involuntary muscle overactivity that develops gradually post stroke. Although considerable research has been devoted to spasticity, the term on itself is inconsistently defined in both literature and clinical practice, and its pathophysiology is still poorly understood. Moreover, agreement on construct-valid outcome measures and effective evidence-based interventions is still lacking in the literature. Current clinical assessment of post-stroke spasticity is restricted to subjective ordinal rating scales, such as the modified Ashworth scale, assessing the total resistance to a manually applied passive joint movement. Unfortunately, this clinical scale is unable to distinguish between muscle overactivity, including spasticity and involuntary background activation, and altered tissue properties, the so-called neural and non-neural components influencing the perceived resistance to passive movement under passive conditions. Moreover, these scales show poor measurement properties with respect to reliability and responsiveness to change. To disentangle increased resistance to passive joint movement, i.e. joint hyper-resistance, in terms of neural and non-neural components is important for understanding underlying neurophysiological mechanisms during upper limb motor recovery and may impact treatment decisions. Instrumented assessment methods have been developed to address the drawbacks of current clinical scales. These methods allow for standardized assessment and can provide objective and quantitative information of the underlying neural and non-neural components of joint hyper-resistance. This thesis investigates instrumented assessment to clinically quantify the underlying neural and non-neural components of wrist hyper-resistance in patients in the subacute and chronic phase post stroke and explores its potential value for timely and patient-specific management of upper limb spastic paresis post stroke.