In the study of 56 patients (37 women), 9 patients (16.1%) had undetectable JCV DNA in CSF and 14 (25%) were asymptomatic for PML. At the time of PML diagnosis, the median age was 45 years, and the median natalizumab treatment duration was 43 months. Results showed that patients with a positive PCR had larger total PML lesion volumes than did those with undetectable JCV DNA (median volume, 22.9 mL vs. 6.7 mL; P = .008). Logistic regression showed that a lower PML lesion volume significantly increased the probability for undetectable JCV DNA.
The research team also observed a positive correlation between PML lesion volume and JCV copy numbers (Spearman’s rho, 0.32; P = .03). PML lesion volume was also higher in patients with PML symptoms and in patients with more widespread lesion dissemination. But no association was found between PCR results and PML lesion dissemination, signs of inflammation, or PML symptoms.
The findings appear to show that patients with a smaller PML lesion volume were more likely to have a negative test result for JCV, which may lead to a delayed diagnosis of PML. Patients with smaller lesion volume were also more likely to be asymptomatic, which may further delay a diagnosis.
“This can result in a therapeutic dilemma. Unjustly excluding PML may have serious consequences (e.g., when switching from [natalizumab] to even more potent immunosuppressive treatments, such as alemtuzumab),” they wrote.