Revised Hammersmith scale for spinal muscular atrophy: Longitudinal changes over six and twelve months in a large international cohort

Abstract

The SMA field is advancing rapidly, with numerous drugs focused on different mechanisms for SMN upregulation now in clinical trials, and with encouraging early results, suggesting the distinct possibility that a clinical improvement may occur as a result of therapeutic intervention. Consequently, there is an increasing demand to demonstrate efficacy by using outcome measures which are ‘fit for purpose’; namely psychometrically robust, clinically meaningful, disease specific and capable of demonstrating improvement. An important characteristic of an SMA outcome measure is the ability to collect relevant information on disease progression over a range of physical activities. The revised Hammersmith Scale for Spinal Muscular Atrophy (RHS) was developed as a psychometrically robust and clinically relevant outcome measure designed to test a broad range of physical abilities seen in children and adults with SMA types 2 and 3. The underlying construct of the scale is a reflective conceptual model of motor performance in SMA. The RHS incorporates revised items from the original Hammersmith Functional Motor Scale Expanded, North Star Ambulatory Assessment, WHO motor milestones, CHOP INTEND and two timed tests; 10 metre run and rise from floor. A large international pilot study of the scale across three collaborating national networks, SMA REACH UK, the Italian SMA network and PNCR SMA Network (USA), in 2015 identified that the RHS is able to capture a broad range of abilities seen in SMA ranging from very weak patients (SMA 1 and 2) to very strong ambulant SMA 3b patients. The pilot study also demonstrated that the RHS is able to distinguish between clinically different groups, it is psychometrically robust from a Rasch perspective, and it has excellent inter and intra-rater reliability. The RHS has continued to be tested across the three networks, and we now present longitudinal data on six and twelve month changes using the RHS in an international cohort of SMA patients.