Incomplete Kawasaki disease presenting as bilateral hip synovitis

A 2-year-old boy presented in a local Emergency Department with 7 days of fever >40.1 C temporarily relieved by antipyretics. He had occasional cough and rhinorrhoea. One day prior to onset of fever, he started limping with no history of trauma, progressing to pain in his right foot on weight-bearing with difficulty mobilising independently. His general practitioner saw him on the second day of his fever and prescribed him amoxicillin and clavulanic acid (Augmentin; Aspen Pharmacare Australia Pty, St Leonards, New South Wales, Australia). The fever persisted for a further 3 days before ceasing the antibiotics with a provisional diagnosis of viral illness. His past medical history was unremarkable. He was born full term without complication. His immunisations were up to date and he had no known allergies. There were no infectious contacts at home; however, he attended day care. On examination, he was febrile (40.1 C) and tachycardic (196 beats/min) returning to the normal range after antipyretics. He looked pale. He had bilateral non-purulent conjunctivitis. He had multiple palpable small cervical lymph nodes with normal ear and throat examination. He had no rashes, other adenopathy or peripheral changes of oedema or desquamation. He had normal respiratory, gastrointestinal and cardiac examination. He was in pain when weight-bearing and dragged his right foot when walking. When sitting, he had normal range of motion in his hips, knees and ankles. He had slightly raised white cell count (WCC) of 14.8 × 10/L with neutrophilic predominance, 9 × 10/L, haemoglobin of 92 g/L and mean corpuscular volume of 78 fL. He had elevated inflammatory markers: c-reactive protein (CRP) was 134 mg/L and erythrocyte sedimentation rate (ESR) was 101 mm/h. Blood culture was sterile. His electrolytes, calcium, magnesium and phosphate, renal and liver functions were normal. Urinalysis, chest x-ray and x-rays of the right hip, tibia/ fibula and femur were normal. He was diagnosed with septic arthritis and transferred to the tertiary centre for orthopaedic management. Further investigations showed persistent anaemia and raised WCC and inflammatory markers. Rheumatologic screen was normal. An ultrasound of both hips showed bilateral small hip effusions and a bone scan was normal. He underwent bilateral hip washout. Fluid from both joints was sent off for culture. The patient was started on intravenous flucloxacillin on admission but was changed to intravenous cephazolin for broader antibiotic coverage. Despite this, he remained febrile for a further 3 days. The cultures of aspirates from both hips were sterile. His WCC and inflammatory markers remained elevated. He remained miserable, lethargic and unable to weight bear. His nasopharyngeal aspirate had negative PCR for influenza, parainfluenza, adenovirus, enterovirus, respiratory syncytial virus, human metapneumovirus, coronavirus, rhinovirus and bocavirus. Medical review after 12 days of fever, raised the high likelihood of KD. Rheumatology review raised the possibility of systemic-onset juvenile idiopathic arthritis (SoJIA). Intravenous antibiotics were ceased and intravenous immunoglobulin (IVIG) and aspirin started. Cardiology review and echocardiogram revealed dilated and ectatic left coronary arteries involving the left main stem coronary artery, left anterior descending artery and circumflex. His fever settled with IVIG treatment. WCC and inflammatory markers normalised over a few days. With ongoing limping, he was given 3 days of IV pulse methylprednisolone. He was mobilising independently and was discharged on prednisolone 1 mg/ kg/day that was weaned over 3 weeks. Aspirin was continued at a low dose cardiology follow-up showed gradual resolution of his aneurysms. Key Points 1 Incomplete Kawasaki disease should be considered in a febrile illness >5 days not responding to appropriate treatment for a presumed cause. 2 There are various multi-systemic clinical features and laboratory findings that can be noted in cases of incomplete Kawasaki disease. 3 It is important to diagnose Kawasaki disease and start treatment early to minimise mortality and morbidity associated with coronary artery changes that are the major sequelae in Kawasaki disease.