Researchers partially characterized the cytochemical content of macrophages containing inclusions, also known as nusinophages, found in the cerebrospinal fluid (CSF) of spinal muscular atrophy (SMA) patients treated with nusinersen (Spinraza®).
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Schafernak et al identified glycosaminoglycans, such as proteoglycans or hyaluronic acid, as one of the main components of nusinophages. On the other hand, they do not contain iron or microorganisms.
Moreover, specimens that contained nusinophages had a higher proportion of macrophages and a lower proportion of lymphocytes than those without nusinophages.
The study authors stated, “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.” They emphasized that this was “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.”
Nusinophages were only visible on Wright-Giemsa staining. They presented with varying sizes and were surrounded by clear vacuoles. On cytochemistry analysis, nusinophages were negative on Prussian blue stain, mucicarmine, Gram stain, Grocott-Gömöri methenamine silver stain, and periodic acid-Schiff stain with and without diastase. They were blue on Alcian blue/periodic acid-Schiff and Alcian blue stain at pH 2.5.
The study, published in Acta Cytologica, included 15 CSF cytology specimens from 8 pediatric patients with SMA receiving nusinersen. Half of the patients, all diagnosed with SMA type 1, had nusinophages.
The presence of macrophages containing peculiar inclusions was first reported in 2018 in the CSF of a child receiving nusinersen. Since then, additional reports have been published. However, it is still unclear whether these cells actually contain nusinersen.
Schafernak KT, Jacobsen JR, Hernandez D, Kaye RD, Perez SE. Cytochemical characterization of cerebrospinal fluid macrophage inclusions in pediatric patients receiving intrathecal nusinersen (Spinraza®) for spinal muscular atrophy. Acta Cytol. Published online August 17, 2021. doi:10.1159/000518005