Achy Leg in a Child

Try out this paediatric case and test your clinical knowledge. The answers are at the bottom.

Questions

A 17yearold boy presents to his GP with a dull ache in his left leg. He reports that the pain used to come and go, but now his leg hurts all the time and is particularly bad at night. He mentions that painkillers don’t seem to help. His mother has noticed that he has been walking funny at football practice for the last couple of weeks and asks if he has sprained something.

PMHx:

Scarlet fever (aged 7)

DHx:Nil

Allergic to ibuprofen

Observations:
SpO2: 99%
Temperature: 37.1
BP: 110/71
HR: 92
RR: 18

Examination:

Pain over distal aspect of femur.

Palpation does not worsen pain.

Antalgic gait noted.

Neurological examination normal

Q1: Should the GP be concerned?

Blood tests and imaging are performed:

Image 1: Case courtesy of Dr Ian Bickle, Radiopaedia.org. From the case rID: 50303

 

Q2: Comment on the blood results.

Q3: Interpret the X-ray. What is the likely diagnosis?

 Q4: What other paediatric condition is classically associated with this condition?

Answers

Reveal the Answers

 Answer to Question 1

The GP should certainly be concerned.There are multiple ‘red flag’ features in his presentation that need further evaluation before a diagnosis of a simple muscular spraincan be made.These include:

Night bone pain

Asymmetrical pain

Intermittent pain that becomes continuous

Pain that is unresponsive to analgesia

A newonset limp

Pain unable to be elicited/worsened with palpation

Unlikely to be an infective cause for pain e.g. septicarthritis (normal observations)

Answer to Question 2

There are several concerning features in these blood results. These include:

Pancytopenia (low Hb, WCCs + plts)this indicates failure of the bone marrow to produce all types of blood cell.

Very high ALP with normal GGTindicates a nonbiliary cause for the raised ALP, in this case most likely a sign of cortical bone destruction

High calcium and phosphate with suppressed PTHthis indicates that the hypercalcaemia is the primary issue and that the parathyroid axis is responding appropriately via negative feedback (PTH increases serum calcium and decreases serum phosphate and is reduced in cases of hypercalcaemia). In this context, the calcium is likely to come from bone resorption.

Combining all these findings, the likely pathology can be isolated to a bony lesion.

Answer to Question 3

This is an AP image of the R knee including the distal femur and proximal tibia + fibula. 

There is an extensive sclerotic disease in the distal femur, with the formation of a Codman’s triangle periosteal reaction.

Diagnosis: Osteosarcoma 

The disease is sclerotic (appears whiter than normal on XR) as osteosarcoma is a cancer of primitive osteoblasts, the cells responsible for bone formation. As such, aberrant multiplication of these cells in cancer produces malignant osteoid which leads to aberrant bone formation and appears whiter on XR – sclerotic. This contrasts with Ewing’s sarcoma, the other major malignant bone tumour in children, which usually presents with a lytic (bone destructive) lesion on XR. Codman’s triangle refers to the area on the medial aspect of the femur where hypoxic changes induced by the tumour leads to aberrant bone formation by the periosteum which is then broken through by the tumour invading into the surrounding tissues, forming a triangle like structure on X-ray.

Answer to Question 4

There is a strong association with retinoblastoma, the paediatric ophthalmological tumour. This is due to the important of the retinoblastoma (Rb) tumour suppressor gene, whose inactivation plays a critical part in driving the disease process for both cancers.

 

Sources:

Image 1: Case courtesy of Assoc Prof Frank Gaillard, <a

href=”https://radiopaedia.org/?lang=gb”>Radiopaedia.org</a>. From the case <a

href=”https://radiopaedia.org/cases/7529?lang=gb”>rID: 7529</a>

 

Dr Amol Joshi
University of Cambridge

About The Author

This case is written by Dr Amol Joshi who has an interest in writing medical puzzles.

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