Systemic juvenile idiopathic arthritis and macrophage activation syndrome: Viva

This oral is built to probe the reasoning that holds the recognition and the early treatment of the macrophage activation syndrome at the centre, and to expose the candidate who has memorised the headline without the corners. The questions escalate from the classification and the pathogenesis to the biologic treatment, the recognition of the MAS, and the management of the paradoxical and the refractory cases. [9]

Opening question: the classification and the pathogenesis

The examiner opens with the presentation and asks how you classify her disease and what the modern understanding of the pathogenesis is. [2]

A strong answer names the ILAR classification of the systemic subtype, with the quotidian fever for at least two weeks plus the arthritis and the extra-articular features, and then the reframing of sJIA as Still disease, the autoinflammatory disease driven by the innate-immune interleukin-one and interleukin-six axis. The interleukin-one-beta drives the quotidian fever and the rash, the interleukin-six drives the acute-phase response, and the interleukin-eighteen primes the immune system for the macrophage activation syndrome. [9]

Model answer. This girl has systemic juvenile idiopathic arthritis by the ILAR criteria, with the quotidian fever, the evanescent rash and the arthritis. The modern understanding is that sJIA is an autoinflammatory disease of the innate immune system, driven by the interleukin-one-beta and the interleukin-six, not the adaptive-autoimmune pathways of the other subtypes. This is why the interleukin-one and the interleukin-six blockade is the first-line treatment. [2][9]

Pitfall probe. Why is the methotrexate less effective for the systemic features of sJIA than for the polyarticular subtypes? Because the methotrexate targets the adaptive immunity, while the systemic features are driven by the innate-immune cytokines. The methotrexate may help the arthritis but not the fever and the rash. [9]

Probe one: the biologic treatment

The examiner presses for the first-line biologic and the dose. [6]

A strong answer names the interleukin-one blockade as the first-line, with the anakinra at one to two milligrams per kilogram per day subcutaneously or the canakinumab at four milligrams per kilogram every four weeks. The tocilizumab at twelve milligrams per kilogram every two weeks for the under thirty kilograms child is the interleukin-six blockade. The glucocorticoids are the bridge. [6][5]

Pitfall probe. What is the advantage of the anakinra over the canakinumab? The anakinra has the rapid onset and the short half-life that allows both the aggressive dosing for the MAS and the rapid withdrawal if the infection is the concern. The canakinumab has the long half-life and the convenience of the monthly dosing. [6]

Probe two: the recognition of the MAS

The examiner asks how you would recognise the macrophage activation syndrome if it develops. [1]

A strong answer reproduces the 2016 criteria and the clinical signs. The fever pattern changes from the quotidian to the persistent. The platelets fall, the ferritin rises sharply, the fibrinogen falls, and the AST rises. The 2016 criteria require the ferritin over six hundred and eighty-four plus any two of the platelet count under one hundred and eighty-one, the AST over forty-eight, the triglycerides over one hundred and fifty-six and the fibrinogen under three hundred and sixty. The falling ESR is the paradoxical sign that the fibrinogen is being consumed. [1][8]

Pitfall probe. Why does the ESR fall in the MAS? Because the fibrinogen that drives the ESR is being consumed, so the ESR falls even as the disease worsens. The candidate who is reassured by the falling ESR in the deteriorating child misses the MAS. [1]

Branch one: the paradoxical MAS under the tocilizumab

The examiner pivots to the scenario where the child is on the tocilizumab and the CRP is normal, and asks how the MAS presents in this setting. [5]

A strong answer names the silent presentation. The interleukin-six blockade suppresses the fever and the CRP, so the usual warning signs are masked. The MAS develops with only the falling platelets and the rising ferritin to betray it. The management is to reduce or to stop the tocilizumab and to add the anakinra and the glucocorticoid. The lesson is the regular monitoring of the ferritin and the platelet trend. [5][10]

Branch two: the refractory MAS

The examiner pivots to the scenario where the MAS does not respond to the glucocorticoids, the ciclosporin and the anakinra, and asks for the escalation. [3]

A strong answer stages the escalation. The anakinra is increased to four to eight milligrams per kilogram per day. The etoposide at one hundred and fifty milligrams per square metre on the HLH-2004 protocol and or the emapalumab, the monoclonal antibody against the interferon-gamma, are considered. The child is in the paediatric intensive care unit. [3][7]

Closing question: the single framework

The examiner closes and asks for the single framework that carries the whole topic. [9]

A strong answer states that sJIA is the autoinflammatory disease driven by the interleukin-one and the interleukin-six, and the macrophage activation syndrome is its interferon-gamma cytokine storm complication. The interleukin-one blockade protects against both, the 2016 criteria give the tool for the early recognition, and the treat-to-target with the early biologic achieves the clinically inactive disease and the glucocorticoid sparing. The candidate who holds the autoinflammatory framework, the 2016 criteria, the interleukin-one-first approach and the paradoxical MAS has the corners that the examination rewards. [9][10]