Validity and Reliability of the Hypertonia Assessment Tool (HAT) in Stroke Patients

Stroke is defined by the World Health Organization (WHO) as a neurological disorder characterized by the sudden onset of focal cerebral dysfunction of presumed vascular origin, lasting at least 24 hours, with no apparent cause other than vascular pathology. It is the second most common cause of death worldwide after cardiovascular diseases and the leading cause of long-term disability in adults. Hemiplegia develops in approximately 75-80% of individuals who experience a stroke, resulting not only in motor impairments but also in a significant decline in quality of life.

A substantial proportion of post-stroke motor impairments is attributable to hypertonia. Hypertonia is a clinical condition characterized by increased muscle tone that limits voluntary motor control and functional movement. The most common subtypes of hypertonia are spasticity, dystonia, and rigidity, each differing in etiopathogenesis, clinical course, and response to treatment. Although dystonia is less frequently recognized compared to spasticity, it may have a considerable impact on functional limitation. Therefore, accurate differentiation of hypertonia subtypes is of great importance for individualized rehabilitation planning, prognostic evaluation, and monitoring treatment effectiveness.

Several clinical assessment tools have been developed to evaluate hypertonia. The Modified Ashworth Scale (MAS), the Tardieu Scale, the Burke-Fahn-Marsden Dystonia Rating Scale (BFM) and the Barry-Albright Dystonia Scale (BADS) are commonly used to assess the severity of hypertonia, spasticity, and dystonic postures. However, these instruments focus solely on the degree of muscle tone and do not differentiate between hypertonia subtypes. None of these measures provide a structured framework for systematically distinguishing clinically distinct subtypes such as spasticity, dystonia, and rigidity. Consequently, uncertainties may arise in both diagnosis and treatment planning.

The Hypertonia Assessment Tool (HAT) was developed in this context as a structured and specific clinical instrument designed to differentiate spasticity, dystonia, and rigidity. The validity and reliability of the HAT have been demonstrated in the pediatric cerebral palsy (CP) population.

However, no validity or reliability study of the HAT has been conducted in adult individuals with stroke, either nationally or in the international literature. Recent systematic reviews on hypertonia assessment have highlighted the insufficient differentiation of spasticity and dystonia in adult populations and the limited use of discriminative clinical tools such as the HAT. This limitation may hinder the implementation of subtype-specific rehabilitation strategies.

Therefore, evaluating the validity and reliability of the HAT in the adult stroke population will add a new dimension to clinical practice by enabling more accurate identification of hypertonia subtypes and contributing to individualized rehabilitation planning. Furthermore, this study will address an important gap in both national and international literature and will provide the first dataset regarding the use of the HAT in adult stroke patients.

Inclusion criteria

• Age 18 years and older
• Clinically and radiologically confirmed diagnosis of stroke (ischemic or -hemorrhagic)
• Brunnstrom stage between 2 and 6
• Presence of post-stroke hypertonia (spasticity, dystonia, or rigidity)
• Cognitive level sufficient to cooperate with assessments (Mini-Mental State Examination (MMSE) score >23 or equivalent clinical evaluation)
• Provision of written informed consent

Exclusion criteria

• Age under 18 years
• Presence of severe accompanying neurodegenerative diseases (e.g., Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis)
• Presence of primary musculoskeletal disorders affecting motor performance (e.g., rheumatologic diseases, fractures)
• Brunnstrom stage of 1
• Severe aphasia, impaired consciousness, or cognitive deficits preventing effective communication and cooperation
• Any psychiatric disorder that may interfere with study participation