Footnotes

• Contributors PR provided clinical care to the patient, obtained consent, oversaw the writing process including formulating the answer, amalgamating input from co-authors and identifying references. GH collated information regarding HIS from identified references and wrote an initial draft description of the condition to utilise in the answer section. SM also provided clinical care to the patient and collated the first draft of the patient history from this. THI provided senior clinical review and provided feedback and improvements to earlier versions of the document.

• 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.

• Provenance and peer review Not commissioned; externally peer reviewed.