Quantitative susceptibility mapping at 7 Tesla in COVID-19: mechanistic and outcome associations, 2023, Rua et al.

SNT Gatchaman

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Quantitative susceptibility mapping at 7 Tesla in COVID-19: mechanistic and outcome associations
Catarina Rua; Betty Raman; Christopher T Rodgers; Virginia F J Newcombe; Anne Manktelow; Doris A Chatfield; Stephen J Sawcer; Joanne G Outtrim; Victoria C Lupson; Emmanuel A Stamatakis; Guy B Williams; William T Clarke; Lin Qiu; Martyn Ezra; Rory McDonald; Stuart Clare; Mark Cassar; Stefan Neubauer; Karen D Ersche; Edward T Bullmore; David K Menon; Kyle Pattinson; James B Rowe

Post mortem studies have shown that patients dying from severe SARS-CoV-2 infection frequently have pathological changes in their central nervous system, particularly in the brainstem. Many of these changes are proposed to result from para-infectious and/or post-infection immune responses. Clinical symptoms such as fatigue, breathlessness, and chest pain are frequently reported in post-hospitalized COVID-19 patients. We propose that these symptoms are in part due to damage to key neuromodulatory brainstem nuclei. While brainstem involvement has been demonstrated in the acute phase of the illness, the evidence of long-term brainstem change on magnetic resonance imaging (MRI) is inconclusive.

We therefore used ultra-high field (7T) quantitative susceptibility mapping (QSM) to test the hypothesis that brainstem abnormalities persist in post-COVID patients and that these are associated with persistence of key symptoms. We used 7T QSM data from 30 patients, scanned 93-548 days after hospital admission for COVID-19 and compared them to 51 age-matched controls without prior history of COVID-19 infection. We correlated the patients’ QSM signals with disease severity (duration of hospital admission and COVID-19 severity scale), inflammatory response during the acute illness (C-reactive protein, D-Dimer and platelet levels), functional recovery (modified Rankin scale; mRS), depression (PHQ-9) and anxiety (GAD-7).

In COVID-19 survivors the MR susceptibility increased in the medulla, pons and midbrain regions of the brainstem. Specifically, there was increased susceptibility in the inferior medullary reticular formation and the raphe pallidus and obscurus. In these regions, patients with higher tissue susceptibility had worse acute disease severity, higher acute inflammatory markers, and significantly worse functional recovery. Using non-invasive ultra-high field 7T MRI, we show evidence of brainstem pathophysiological changes associated with inflammatory processes in post-hospitalized COVID-19 survivors.

This study contributes to understanding the mechanisms of long-term effects of COVID-19 and recovery.


Link | PDF (Preprint: MedRxiv)
 
The current study provides imaging evidence for mid-to-long term microstructural abnormalities in the brainstem following COVID-19 hospitalization. Our key findings are that in COVID-19 survivors, multiple regions of the medulla oblongata, pons and midbrain show magnetic resonance susceptibility abnormalities at a median time of 6.5 months from hospital admission.

We hypothesise that a brainstem insult occurs in hospitalized COVID-19 patients, impairing autonomic functions that contribute to persisting clinical symptoms. In part, a similar pattern is observed following post severe traumatic brain injury, with patients reporting fatigue, dizziness, but also tachycardia, tachypnoea and hypertension, linked to acute or chronic brainstem dysfunction.

Neuropathological changes in the brainstem in patients with COVID-19 have been detected in post mortem cases. In most cases, there is no evidence of direct viral infection of the CNS, but rather a neuroinflammatory response to systemic infection.

We show that the brainstem is a site of vulnerability to long term effects of COVID-19, with persistent changes evident in the months after hospitalization. These changes are hypothesised to be driven by neuroinflamatory responses, and more evident in patients with longer hospital stays, higher COVID severity, more prominent inflammatory responses, and worse functional outcomes. Ultra-high field 7T QSM was sensitive to these pathological changes in the brainstem, which could not be detected at standard clinical field strengths.
 
"Cause of long COVID in patients uncovered..." - the media coverage is rather overhyped. The post-COVID patient population was small (n=31) and also a post-hospitalisation cohort (so likely quite different to LC-ME/CFS), the technique used is not sufficient to delineate past inflammatory injury from ongoing inflammation, and each patient was also only scanned once (at on average 219 days from admission). It's certainly an interesting result but "bombshell" is not the word I'd use.
 
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