A previously well 7-year-old girl presented with a 6-week gradual history of progressive lip swelling with oral mucosal discomfort (figure 1). There was no precipitating factor identified. She was systemically well. There was no history of mucosal ulceration, abdominal pain, diarrhoea, skin rashes, atopy or weight loss. She recently received oral antibiotics for the perioral swelling with little effect and was on no regular medication. There was no significant family history including autoinflammatory conditions nor exposure to tuberculosis.

Significant lip and perioral tissue swelling at presentation.

Examination revealed weight and height on second centiles. Perioral inspection revealed swelling of both lips and perioral tissues, angular cheilitis, lower lip fissures and erythema. Intraoral examination revealed oral mucosal and gingival inflammation. Systems examination, including perianal examination, was unremarkable.

Which initial next step would be the single most appropriate in this case?

Blood tests including full blood count, iron profile, micronutrient screen and stool for faecal calprotectin.

Blood tests including serum IgE levels, compliment levels (C3/C4), and C1-esterase inhibitor (C1-INH) protein and function.

Mucosal swab for viruses including herpes simplex virus (HSV), …