Table 5 Rare disease patients shed light on blind spots and assist in instrument troubleshooting [87,88,89]

Disease context: Amyotrophic lateral sclerosis (ALS) is a neurological disease that attacks the motor neurons, the cells that the brain uses to keep muscles moving. Over the course of three to five years, people with ALS progressively lose the ability to move their fingers and toes, their arms and legs. Then they lose the ability to speak, to turn their head, and to swallow food. When the diaphragm and chest muscles give out, they can no longer breathe and die.

A legacy instrument: The Amyotrophic Lateral Sclerosis Functional Rating Scale – Revised (ALFRS-R) is an established rating scale for measuring the global function of patients with ALS.

Gaps identified and troubleshooting: When Cathy (a research psychologist affected by advanced ALS) came to complete the ALSFRS-R she was frustrated that despite her ability to participate in family life and write poetry (with the aid of assistive technology, such as an eye tracking machine and a computer to communicate), the scale reflected her as ‘a zero’. When answering the questionnaire:

 - ‘Compared to the time before you had symptoms of ALS [...] have you noticed any changes in your speech?’ She could no longer speak. Zero point.

 - ‘Have there been any changes in your ability to swallow?’ She hadn’t swallowed in years. Zero point.

 - ‘Has your ability to walk changed?’ She could not walk or move her legs. Zero. etc.

Resolution: Though a valuable rating instrument, ALFRS-R was deemed not fit-for-purpose in advanced stages of disease. In response, Cathy reached out to the online community PatientsLikeMe to develop new items with input from over 300 ALS patients. Three new items were selected, relating to: the ability to show emotional expression in the face, the ability to use fingers to manipulate devices, and ability to get around inside the home. Subsequent research using Rasch analysis confirmed that a refinement of ALFRS-R was required. The ALSFRS Extension is now used in ALS research.