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]

SAQ 2 (10)

A fifteen-year-old boy presents with three months of worsening pain around the right knee, now waking him from sleep and not relieved by rest, and a firm, deep, fixed swelling over the distal femur. A plain radiograph shows a mixed lytic and sclerotic destructive lesion in the distal femoral metaphysis with a sunburst periosteal reaction and a Codman triangle. The on-call surgical team has booked an incisional biopsy in a peripheral hospital for tomorrow. [8] [9]

a) Name the most likely diagnosis and give the two radiographic features that support it, relating them to the tumour biology. (3 marks) [8]

b) Explain why the planned peripheral biopsy must be cancelled and state the correct principle governing biopsy of a suspected primary bone tumour, with the harm it prevents. (3 marks) [8]

c) Describe the definitive treatment pathway for this tumour, naming the neoadjuvant chemotherapy backbone and the histological threshold that defines a good response. (2 marks) [9]

d) Separately, describe the emergency management of a child who presents with back pain and a new leg weakness and bladder incontinence, and the diagnosis you must assume. (2 marks) [9]