Real‐world challenges in the diagnosis of primary progressive multiple sclerosis

Background and purpose Despite the 2017 revisions to the McDonald criteria, diagnosing primary progressive multiple sclerosis (PPMS) remains challenging. To improve clinical practice, the aim was to identify frequent diagnostic challenges in a real‐world setting and associate these with the performance of the 2010 and 2017 PPMS diagnostic McDonald criteria. Methods Clinical, radiological and laboratory characteristics at the time of diagnosis were retrospectively recorded from designated PPMS patient files. Possible complicating factors were recorded such as confounding comorbidity, signs indicative of alternative diagnoses, possible earlier relapses and/or incomplete diagnostic work‐up (no cerebrospinal fluid examination and/or magnetic resonance imaging brain and spinal cord). The percentages of patients fulfilling the 2010 and 2017 McDonald criteria were calculated after censoring patients with these complicating factors. Results A total of 322 designated PPMS patients were included. Of all participants, it was found that n = 28/322 had confounding comorbidity and/or signs indicative of alternative diagnoses, n = 103/294 had possible initial relapsing and/or uncertainly progressive phenotypes and n = 73/191 received an incomplete diagnostic work‐up. When applying the 2010 and 2017 diagnostic PPMS McDonald criteria on n = 118 cases with a full diagnostic work‐up and a primary progressive disease course without a better alternative explanation, these were met by 104/118 (88.1%) and 98/118 remaining patients (83.1%), respectively (p = 0.15). Conclusion Accurate interpretation of the initial clinical course, consideration of alternative diagnoses and a full diagnostic work‐up are the cornerstones of a PPMS diagnosis. When these conditions are met, the 2010 and 2017 McDonald criteria for PPMS perform similarly, emphasizing the importance of their appropriate application in clinical practice. In a real‐world cohort of designated PPMS patients, a critical review of the medical files shows multiple factors that complicate the diagnosis, mostly concerning the progressive disease course from disease onset and completeness of diagnostic work‐up. After censoring patients with such complicating factors, the fulfillment of the McDonald criteria increases from less than 75% to almost 90%. This indicates that a thorough review of the clinical course and a complete diagnostic work‐up are essential for a definite PPMS diagnosis.