Study Validates First Disease-Specific PRO Instrument for Patients With Congenital TTP

Clinicians now have a new way to better understand the experiences of patients with congenital thrombotic thrombocytopenic purpura (cTTP).

A new study, published in Journal of Patient-Reported Outcomes, evaluated the psychometric properties of the cTTP Patient Experience Questionnaire (cTTP-PEQ) and found that it is a meaningful tool with which to gauge patients’ experiences with the ultra-rare disease.

TTP is caused by a deficiency in the clotting enzyme ADAMTS13, which can cause life-threatening clot formations in the small blood vessels in major organs. The study investigators said approximately 1 in 1 million people have a congenital form of the disease. In those patients, the disorder is caused by a mutation in the gene that encodes ADAMTS13, they said.

Aside from an increased risk of severe health events, like myocardial infarction or neurologic abnormalities, the authors said cTTP can have a major impact on patients’ quality of life.

“Patients experience numerous disease-related complications, and patient-reported complaints often include fatigue, headache, abdominal pain, bruising, cognitive impairment, and experience of depression and mood alterations,” they wrote.

There is no therapy approved specifically for TTP, the investigators said, although many patients receive prophylactic plasma infusion and/or concentrates of von Willebrand factor and factor VIII. Some of those treatments lead to adverse events or other limitations that can affect patients’ quality of life.

For those reasons, the authors said, it is important for clinicians to have a useful instrument with which to track patient-reported outcomes (PROs). In the past, clinicians have used generic health care–related QOL (HRQOL) instruments or instruments developed for other blood disorders in patients with cTTP. However, such instruments do not account for the full burden of cTTP, the authors argued, given that they were not specifically developed for the disease.

In a previous report, investigators developed a conceptual model to capture the symptoms and effects of cTTP. That model was then used to create a draft instrument, the 26-item cTTP-PEQ. The purpose of the current study was to assess the instrument’s ability to assess psychometric validity of the instrument and compare it to other measures of PROs.

Thirty-six patients participated in the study. All had a diagnosis of cTTP and were receiving treatment. Participants were asked to complete self-administered PRO assessments, including the cTTP-PEQ, at baseline and at day 14. The authors then analyzed those responses to see how well the instruments captured patients’ experiences.

The investigators found that the cTTP-PEQ was valid and reliable in assessing the experiences of the cohort, suggesting it can be a useful tool for tracking patients’ daily experiences and their responses to treatment changes.

They said the study had important limitations, largely due to the difficulty of recruiting a significant number of patients with the ultra-rare disease. Three-quarters of patients were receiving prophylactic treatment and most participants did not modify their treatment during the study. In addition, most patients in the study only reported mild symptoms. The authors noted that severe cTTP has a high mortality rate.

“Ideally, modern test theory methods would be used to further examine the alignment of the response options with patient severities and assess replicability of the findings,” they said. “However, these methods would require larger sample sizes.”

Although their small sample size resulted in significant limitations, the authors said their findings ultimately support the use of the cTTP-PEQ, making it the first validated PRO instrument developed specifically for cTTP.

“This instrument has the potential to aid our understanding, measurement, and interpretation of the effect of new treatments and how they can improve patients’ HRQOL,” they concluded.

Reference

Oladapo A, Ito D, Rodriguez AM, et al. Psychometric evaluation of a patient-reported outcomes instrument for congenital thrombotic thrombocytopenic purpura. J Patient Rep Outcomes. Published online July 14, 2023. doi:10.1186/s41687-023-00592-w