Hand-foot-and-mouth disease and enterovirus infection — branching viva

Opening question

Examiner: Take me through this child. What is going on, and what is your frame? [2]

Candidate: This is enterovirus 71 brainstem encephalitis complicating hand-foot-and-mouth disease. The classic vesicular rash on day three, plus sleep myoclonus and ataxia, is the textbook early presentation of EV71 reaching the brainstem. My frame is two-layered: confirm the diagnosis and grade the neurological severity, and get this child into a monitored bed with PICU alerted, because the interval between a tremor and neurogenic pulmonary oedema can be short. I would admit, send PCR and imaging, and observe continuously. [2] [5]

Examiner: Why is this child at particular risk? [1]

Candidate: The burden and the mortality of EV71 fall on children under five, and especially under two, because of immature immunity, small physiological reserve and close-contact behaviours that maximise transmission. In this age group the same brainstem injury that produces myoclonus and ataxia progresses more readily to autonomic dysregulation and pulmonary oedema. The host turns a neurotropic virus into a lethal one. [1] [2]

Branch 1 — pathophysiology

Examiner: Explain how enteroviruses cause HFMD, and why EV71 is different. [1]

Candidate: Non-polio enteroviruses enter through faecal-oral, respiratory droplet and vesicle-fluid contact and replicate first in the gut and upper-respiratory epithelium. A short viraemia seeds the skin and mucosa, and viral replication in basal epithelial cells produces the virus-rich vesicles. Coxsackievirus A16 and A6 largely stay confined to skin and mucosa, which is why they are usually mild. Enterovirus 71 is different because it is neurotropic: it enters the central nervous system via cranial and peripheral nerves and targets the brainstem. [1] [8]

Examiner: What is the mechanism of death in severe EV71 disease? [7]

Candidate: Injury to the medullary autonomic centres triggers a sympathetic storm with hypertension and vascular leak that floods the lungs with protein-rich fluid — neurogenic pulmonary oedema. That is the terminal event, and it is why a child can be playing one day and in cardiopulmonary failure the next. Studies of EV71 encephalitis with cardio-respiratory compromise identified elevated interleukin-1β and related cytokines as markers of poor prognosis, reflecting the inflammatory drive behind this autonomic collapse. [7] [2]

Branch 2 — diagnosis

Examiner: How will you confirm EV71 in this child? [5]

Candidate: I would send vesicle fluid, throat and stool for enterovirus PCR with EV71 subtyping. Vesicle fluid is highly sensitive while lesions are present, throat captures early replication, and stool stays positive for weeks because enteroviruses are shed through the gut. After stabilisation I would arrange lumbar puncture and magnetic resonance imaging — the CSF may show lymphocytic pleocytosis with possible EV71 PCR, and MRI may demonstrate characteristic brainstem signal change. An N-terminal pro-B-type natriuretic peptide can be sent as a prognostic marker. [5] [7]

Examiner: If the rash were atypical and widespread rather than acral, what would you consider? [8]

Candidate: I would consider coxsackievirus A6 atypical HFMD, which produces widespread vesicles and bullae beyond the palms and soles, often over eczema (eczema coxsackium), and is followed weeks later by nail shedding (onychomadesis). The key is to distinguish it from Stevens-Johnson syndrome, which has target lesions and severe mucosal destruction and needs urgent immune therapy — whereas CVA6 HFMD is managed supportively. [8] [2]

Branch 3 — treatment and the critical-care strategy

Examiner: How will you manage the autonomic and respiratory risk in this child? [7]

Candidate: The haemodynamic strategy is specific to EV71 brainstem disease. Because the failure is sympathetic overdrive with vascular leak, I would use judicious fluid restriction with milrinone and vasoactive support rather than generous fluid boluses, which would worsen pulmonary oedema. I would secure the airway early and ventilate with lung-protective settings at the first sign of pulmonary oedema, and mobilise ECMO capability for refractory cardiopulmonary failure. There is no proven antiviral; intravenous immunoglobulin is used empirically on weak evidence. [7] [8]

Examiner: Why milrinone, and why avoid the fluid bolus? [7]

Candidate: Milrinone, a phosphodiesterase inhibitor, reduces the sympathetic surge and supports cardiac output, which fits a brainstem-driven failure rather than primary pump failure. The instinct to bolus fluid as one would in sepsis is the specific error here — the leak from autonomic dysregulation turns a generous bolus into worse pulmonary oedema, so the evidence-based approach is restriction and inotropy. [7] [2]

Branch 4 — public-health layer

Examiner: Walk me through the infection-control and public-health response. [1]

Candidate: I would maintain contact and droplet precautions while the child is unwell, and advise childcare exclusion until lesions have healed or are covered. I would reinforce household hand hygiene — soap and water, not just alcohol gel, because alcohol does not fully eliminate non-enveloped enteroviruses — and counsel the family on the red flags. If this is part of a cluster, I would notify the public-health unit and arrange serotype surveillance on representative cases, because knowing whether the season is EV71 or coxsackievirus shapes the admission threshold for every child across the service. [1] [8]

Examiner: Who in the household needs particular attention? [1]

Candidate: The youngest contacts — especially infants — are the priority, because they carry the mortality risk. I would counsel the family to watch the infant sibling closely for poor feeding, drowsiness, weakness or breathing difficulty and to bring them in promptly. Pregnant household members should be reassured with careful safety-netting; there is no specific intervention beyond hygiene, and no routine vaccine to offer. [1] [2]

Branch 5 — prevention and the vaccine

Examiner: Is there a vaccine, and why might this child not have been protected? [8]

Candidate: Two large phase-3 trials published in 2014 — Zhu and colleagues and Li and colleagues — showed that inactivated enterovirus 71 vaccines protect against EV71-associated HFMD and its neurological complications, and these vaccines are licensed in China. The WHO, following the 2016 SAGE review, endorses their use in high-burden settings. But the vaccines are not in routine schedules in Australia, Aotearoa New Zealand, the UK, the US or Canada, so this child would not have been offered one — and the vaccines are serotype-specific and do not cover coxsackieviruses. [8] [1]

Examiner: So what does prevention look like in your region? [1]

Candidate: In my region prevention rests on hygiene, childcare exclusion, outbreak surveillance and clinician vigilance for the EV71 neurological signs — not on routine vaccination. Soap-and-water handwashing, surface cleaning of shared toys, exclusion of unwell children, and early recognition of brainstem signs are the practical tools, and the aim is always to protect the youngest, least-protected members of each household and classroom. [1] [8]

Wrap

Examiner: Summarise the HFMD and enterovirus stance in one sentence. [2]

Candidate: Recognise HFMD as a common enterovirus illness that is mild for coxsackieviruses but lethal when enterovirus 71 reaches the brainstem, watch for myoclonus, ataxia, weakness and autonomic instability, confirm with PCR and imaging, manage mild disease supportively and severe EV71 disease with fluid restriction, milrinone and lung-protective ventilation, prevent spread through hygiene and exclusion, and know that the inactivated EV71 vaccines work but are not yet part of routine schedules in my region. [2] [8]