Cytochemical Characterization of Cerebrospinal Fluid Macrophage Inclusions in Pediatric Patients Receiving Intrathecal Nusinersen (SPINRAZA®) for Spinal Muscular Atrophy

Abstract

<b><i>Introduction:</i></b> Spinal muscular atrophy (SMA) is a debilitating neuromuscular disorder caused by biallelic deletion of the <i>SMN1</i> gene. Nusinersen, an antisense oligonucleotide delivered intrathecally, binds to the pre-mRNA of <i>SMN1</i>’s pseudogene, <i>SMN2</i>, to prevent exon skipping and produce functional SMN protein to compensate for the deficiency caused by <i>SMN1</i> deletion. <b><i>Case Presentation:</i></b> We reviewed 15 cerebrospinal fluid (CSF) cytology specimens from 8 patients receiving nusinersen for SMA. Macrophages with peculiar inclusions (“nusinophages”) were seen in 8 specimens from 4 of the patients: 1 infant and 3 children with SMA type 1. This finding has only previously been reported in adults with SMA types 2 and 3 and in 2 infants with SMA type 1. <b><i>Discussion/Conclusion:</i></b> Specimens containing nusinophages had a significantly higher proportion of macrophages and lower proportion of lymphocytes than those in which nusinophages were not detected. The macrophage inclusions do not represent iron or microorganisms and instead are composed, at least in part, of glycosaminoglycans. Because CSF is a common specimen type, cytotechnologists and cytopathologists need to be aware of these inclusions, so they do not interpret them erroneously as evidence of infection or hemorrhage, especially in light of the fact that oligonucleotide therapy has been approved for a variety of conditions and is currently under investigation for intrathecal delivery in several other neurodegenerative disorders.

What could be the function of the spinal muscular atrophy-causing protein SMN in macrophages?

“…Interestingly, SMA patients treated with the ASO Nusinersen showed macrophages with dark inclusions in the cerebrospinal fluid (CSF). After treatment, the CSF showed unique inclusions comprised of glycosaminoglycanes in macrophages, which were most likely monocyte derived ( 93 , 94 ). Another study reported an increase in IL1ß, IL23 and IL6, which can be produced by macrophages, in sera of pediatric and adult SMA patients type I-III treated with Nusinersen ( 95 ).…”

Molecular markers of disease severity and response to nusinersen therapy in 5q spinal muscular atrophy (literature review)

“…Нервно-мышечные Б О Л Е З Н И Neuromuscular DISEASES 3'2023 ТОМ 13 VOL. 13 отмечалось повышение в ЦСЖ уровня лейкоцитов, общего белка и даже появление олигоклонального типа синтеза, а также макрофагов с вакуолями, что может означать их активацию и/или фагоцитоз ими препарата [14,[29][30][31][32][33]. Впрочем, повышение концентрации общего белка в ЦСЖ может быть прямым следствием повышения активности белка выживаемости мотонейронов [29].…”