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Dear Editor,
We read with interest the correspondence by Chen et al 1 about our recent article on the comparison of clinical, laboratory and artificial intelligence–radiological findings in patients with lung involvement either from macrophage activation syndrome (MAS), a secondary form of haemophagocytic lymphohistiocytosis (HLH) or severe coronavirus disease 2019 (COVID-19).2
Age is one of the most common confounding factors in any observational study since it is associated with an increased risk of comorbidities, which may influence the outcome. In our study, the matching for age was not reliable because of higher prevalence of severe COVID-19 in elderly patients, who were admitted to intensive or subintensive care units of our hospital. These results mirror what was already observed in other observational studies,3 4 in which the incidence and severity of COVID-19 are generally higher in elderly patients due to higher frequency of comorbidities, increased frailty and immunosenescence.5 Conversely, MAS complicating adult-onset Still’s disease (AOSD), as patients assessed in our study, usually affects young adults.6 Considering the scientific debate behind our study,2 about the possibility that severe COVID-19 could be considered or not part of HLH spectrum, the age of occurrence may further differentiate the clinical pictures between these diseases.
Furthermore, Chen et al 1 questioned the use of Yamaguchi criteria in classifying AOSD patients .7 Although …
Footnotes
Handling editor Josef S Smolen
PR and FB contributed equally.
AB and RG contributed equally.
Contributors All the authors meet all criteria for authorship in the ICMJE Recommendations, since all authors made substantial contributions to the conception or design of the work, and the acquisition and interpretation of data. All authors contributed to the critical review and revision of the manuscript and approved the final version. All the authors agreed to be accountable for all aspects of the work.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, conduct, reporting or dissemination plans of this research.
Provenance and peer review Commissioned; internally peer reviewed.