Two previously well Caucasian teenage girls with no significant travel or family history were admitted with sinusitis refractory to treatment with antibiotics. Both had progressive symptoms despite broad-spectrum antibiotics and developed involvement of other systems, ultimately requiring admission to the paediatric intensive care unit (PICU). They were subsequently diagnosed with the same condition and made an excellent recovery.The first girl, 14 years old, originally presented to her general practitioner with a sore throat, nasal congestion, and fever. Despite multiple courses of antibiotics over the following month she presented again multiple times with progressive symptoms including epistaxis, widespread myalgia and arthralgia, difficulty in breathing, haemoptysis, fatigue, and weight loss. Examination on admission found minimal discharge from her right tympanic membrane, ulcerated inferior turbinates with dried blood and yellow mucus in both nasal cavities, swollen tonsils without exudate, and an isolated aphthous ulcer on the tip of her tongue. She had small bilateral cervical lymph nodes. Examination of the cardiovascular system was unremarkable but on respiratory examination there was reduced air entry on the right side. Her abdomen was generally tender but soft with no organomegaly. A week into her admission she developed an oxygen requirement and increased work of breathing requiring intubation and ventilation.The second girl, 13 years old, presented to her local hospital with a 1-day history of epistaxis, right ear pain, and pain and swelling to the right periorbital tissues. Again, despite multiple courses of antibiotics, she had persistent symptoms and subsequently developed fever, fatigue, haemoptysis, and had a syncopal episode. She was admitted to her local district general hospital and, despite initial treatment, deteriorated over the following 2 weeks with persistent fever, new oxygen requirement, deteriorating renal function, and anaemia. She was transferred to a tertiary centre for respiratory support which escalated from Optiflow, through continuous then biphasic positive airway pressure, intubation and ventilation, and ultimately VV-ECMO.The investigations for both patients prior to admission to PICU at our centre are shown in table 1.edpract;107/2/113/T1T1T1Table 1Investigations Case 1 Case 2 Haematology Leucocyte peak (×109/L) 18.3 19.0 Neutrophil peak (×109/L) 15.2 13.7 Lymphocyte peak (×109/L) 3.5 2.3 Eosinophil peak (×109/L) 0.9 2.5 Platelets Normal Normal Haemoglobin nadir (g/L) 79 74 ESR (mm/hour) 104 44 Biochemistry Creatinine peak (umol/L) Normal 153 CRP peak (mg/l) 321 280 ALT (IU/L) 122 Normal Microbiology Nasal swab: Moraxella catarrhalis Ear swab: Pseudomonas aeruginosa Sputum negative for acid-fast bacilli, PCR negative ASOT 1600 IU/ml No growth on blood or urine culture Negative viral throat swab and MCS throat swab No positive microbiology including Monospot, Mantoux and TSpot Urine dipstick On day of admission: 1+pro, 4+Hb, 2+leu, 2+ket One week into admission: 3+pro, 4+Hb, 2+leu, 2+ket Three days prior to admission: 2+Hb, otherwise normal Radiology Echocardiogram: normal CXR at admission: normal CXR after 1 week: see figure 1 CT head: pansinusitis Abdominal USS: mild hepatomegaly, diffusely echogenic kidneys Echocardiogram: normal CT chest at local hospital: see figure 2 CXR on admission to PICU: bilateral consolidation with rounded lucency in right lower zone suggestive of cavity formation ALT, alanine aminotransferase; ASOT, anti-streptolysin O titre; CRP, C-reactive protein; CT, computed tomography; CXR, chest X-ray; ESR, erythrocyte sedimentation rate; Hb, haemoglobin; leu, leucocytes; ket, ketones; MCS, microscopy, culture, and sensitivity; PICU, paediatric intensive care unit; pro, protein; TSpot, measures T lymphocytes primed to Mycobacterium tuberculosis antigens; USS, ultrasound scan. QUESTIONS: Describe findings in figures 1 and 2.Which causes of sinusitis could explain the presentation of both cases?Acute sinusitis following viral upper respiratory tract infection.Bacterial infection.Allergic sinusitis secondary to mould.Underlying diagnosis of cystic fibrosis.Sarcoidosis.Tuberculosis.Granulomatosis with polyangiitis.Samter's triad.Ciliary dysfunction.Immunodeficiency.What investigations should be performed in a child presenting with symptoms of sinusitis?edpract;107/2/113/F1F1F1Figure 1The chest X-ray for case 1, 1 week into her hospital admission.edpract;107/2/113/F2F2F2Figure 2The chest CT for case 2 at her local hospital, prior to transfer. Answers can be found on page XX. [ABSTRACT FROM AUTHOR]