Children presented with similar symptoms. Respiratory symptoms are usually subtle and mild. These can include tachypnea, hypoxia (43% in the Stanford series), and pulmonary hypertension (30% in the Stanford series).
Digital clubbing, often with erythema, was a common finding. Some children showed pruritic, nonevanescent rashes. Eosinophilia occurred in 37% of the Stanford series and severe abdominal pain in 16%, although Dr. Mellins noted that belly pain may be underestimated, as it was only volunteered, not queried, information.
“There are some red flags that should raise suspicion even without obvious respiratory symptoms,” Dr. Mellins said. These include lymphopenia, unexplained abdominal pain, eosinophilia, an unusual rash, and finger clubbing with or without erythema.
Findings on imaging were consistent in both series. Several key clinic features emerged: pleural thickening, septal thickening, bronchial wall or peribronchovascular thickening, “tree-in-bud” opacities, “ground-glass” opacities, peripheral consolidation, and lymphadenopathy.
“The imaging findings correspond to two things,” Dr. Schulert said. “The first is inflammation in the interstitium, which is evidence of chronic and ongoing inflammation. The other thing is that the alveoli are filled with a lipoproteinaceous material which is actually surfactant that’s not being normally recycled by the lung macrophages. You can see these features in other conditions where there’s a problem with lung macrophages, like pulmonary alveolar proteinosis, genetic and autoimmune disorders, infections, or inhalants.”
Pathology showed alveolar filling – a location in the lung that hides usual symptoms until the lung disease is advanced. Prior drug reactions were common. Tocilizumab anaphylaxis occurred in close to 40% of the Stanford series – a surprising finding given the 0.6% reaction incidence in the drug’s sJIA trials. Dr. Schulert saw a similar story.
“In our cohort we also observed a striking number of adverse events to cytokine-targeted biologics exposure,” Dr. Schulert said. “Most of these reactions were to tocilizumab, and were described variously from pain and feeling unwell, to difficulty breathing, to anaphylaxis.”
In a risk analysis, Dr. Schulert determined that adverse events to cytokine-targeting biologics increased the likelihood of lung disease more than 13 times (odds ratio, 13.6).
“We also identified a statistically significant association with history of macrophage activation syndrome when compared to controls (OR, 14.5),” Dr. Schulert and associates wrote.
Both the Cincinnati and Stanford teams conducted genetic analyses on some of their patients.
Among eight lung biopsy samples, Dr. Schulert found 37 differentially expressed genes: 36 with increased expression and 1 with decreased expression. Many of the up-regulated genes are involved in interferon-gamma response. Two (CXCL10 and CXCL9) are interferon-induced chemokines associated with macrophage activation syndrome. The down-regulated gene, PADI4, modulates immune response in lupus, and has been associated with the risk of interstitial lung disease in RA.
Dr. Mellins and her team analyzed whole-exome sequencing data from 20 patients and found some rare protein-altering gene variants in genes related to pulmonary alveolar proteinosis, all of which were heterozygous and shared with a healthy parent. But none of them could be directly tied to the disorder.
Another genetic puzzle demands attention, she said. About 10% of the children had trisomy 21 – a stark contrast to the typical 0.2% prevalence among a control group of sJIA patients without any known lung disease in the Childhood Arthritis and Rheumatology Research Alliance Registry cohort, similar to the background population rate. There were suggestions of more aggressive lung disease in all six of these children. Four presented with hypoxia, and two showed advanced interstitial fibrosis. Children with trisomy 21 also seemed more susceptible to infections; 83% had a viral or fungal lung infection at diagnosis, compared with 29% of those without trisomy 21.