Limp and Night Pain
SR is a 15 year old boy. He presents with a poorly localizing pain in the region of the right lower thigh and knee of 2 months duration. The father recalls a fall in school a year prior and the pain started some time after the fall. The pain is generally constant but often wakes the boy at night.
Repeated blood tests have shown normal full [complete] blood counts, acute phase reactants (ESR) and X rays / MRI of the knee. He has received various diagnostic labels before presentation including being a possible malingerer who wishes to avoid school.
Examination reveals an alert but visibly disturbed teenager who walks in with an antalgic gait (limp). He has mild wasting of the muscles of the mid-thigh on the right side which is confirmed on measurement of mid-thigh circumference on both sides. Joint examination is normal. MRI of the hip reveals an osteoid osteoma near the upper end of the femur. An orthopedic referral and subsequent excision provides long term relief.
This case illustrates several important learning points;
- Many cases of limp or limb pain are attributed to trauma which actually is insignificant or eventually irrelevant to the final diagnosis.
- Nocturnal bone pain (a red flag symptom) should alert to the possibility of osteoid ostema or malignancy. Pains that wake a child from sleep at night exclude functional causes. Typically the pain from osteoid osteomas respond to NSAIDS but this is not diagnostic.
- Subtle physical findings – in this case the mild wasting of the mid-thigh, give a valuable clue to the diagnosis.
- Hip examination (see pGALS pREMS-hips) is important and reduced internal rotation is the first movement to be restricted with hip disease irrespective of the cause.
- Pain originating in the region of the hip may be referred to the knee.
- The presentation is not consistent with growing pains – the rules of growing pains are useful and this patient ‘breaks’ several of the rules. Targeted investigation after localizing the origin of the pain easily reveals the diagnosis in most cases – radiographs may show subtle changes which can be missed. Further imaging is often revealing - MRI of the hip revealed the pathology in this boy
- The assessment of a limping child is ideally performed by a specialist with experience in paediatric musculoskeletal medicine – rheumatology or orthopaedics although it is important that a rheumatology opinion is sought before embarking on invasive investigations. Many children with limp are referred to orthopaedics as the point of first contact even though orthopaedic causes account for only a minority of cases.
The MRI below shows an osteoid osteoma (arrowed) in the proximal femur with surrounding enhancement and bone oedema.