Progressive post infectious neurological syndromes with a poor outcome: Long term follow-up and neurofilament light chain quantification

Postinfectious neurological syndromes (PINS), among which acute disseminated encephalomyelitis (ADEM), are inflammatory and mostly monophasic disorders. We previously reported that PINS patients can show relapses, or even disease progression. Here we describe a cohort of patients with progressive-PINS and >5 years of follow-up, that developed a progressive worsening without radiological/cerebrospinal fluid analysis evidence of inflammation. At onset 5 patients fulfilled diagnostic criteria for ADEM and none for MS. Progression occurred after a median of 22 months from onset (in 4/7 after 1/more relapses), manifesting as ascending tetraparesis with bulbar functions involvement in 5/7. Five/7 patients received high dose steroids and/or IvIG and 6/7 Rituximab (n = 4) and/or cyclophosphamide(n = 2), with no impact on disease progression in 6/7. NfL levels were higher in patients with progressive-PINS compared to monophasic-ADEM (p = 0.023) and healthy controls (p = 0.004). Progression is rare, but possible, in PINS. Immunotherapy seems to be ineffective in these patients, and elevated serum NfL in serum suggest persistent axonal damage.