Bone pain and malignancy red flags — formative SAQs

SAQ 1 (10)

A four-year-old girl is referred to the outpatient clinic with a working diagnosis of monoarticular juvenile idiopathic arthritis affecting the right knee, present for seven weeks. On your assessment she has no morning stiffness, the pain is deep and in the distal thigh rather than the knee joint, she looks pale and tired, and you find cervical lymphadenopathy and a few bruises. A full blood count shows a haemoglobin of 90 g/L, a platelet count of 62 times ten to the ninth per litre, and a white cell count of 3.4 times ten to the ninth per litre. ^{[2] [1]}

a) State the diagnosis that this pattern most strongly suggests and the single most important discriminator against juvenile idiopathic arthritis. (2 marks) ^[2]

b) List the four discriminating features from the Jones multicentre case-control study that favour childhood leukaemia over juvenile idiopathic arthritis, and explain why a low platelet count is particularly discriminating. (4 marks) ^[2]

c) State the same-day radiographic investigation you would request and the characteristic plain-film finding of leukaemic infiltration, naming the eponymous sign and the study that established it as a discriminator. (2 marks) ^[3]

d) Outline your immediate management and disposition, including the test that confirms the diagnosis and the team to whom you refer. (2 marks) ^[1]