PAINFUL LIMB IN SICKLE CELL DISEASE
A 15-year-old boy with known sickle cell disease, presents to the emergency department with pain in his right leg. The pain has been worsening over the last 4 days and he is now barely able to walk. He has an associated fever and lethargy. There is no reported history of trauma and he is taking prophylactic penicillin.
His temperature is 37.8°C and pulse rate 114/min. His oxygen saturations are 91 per cent on room air. He looks unwell and is in severe pain. There is no obvious abnormality of his right leg. He has significant tenderness over his right thigh. He has normal knee and hip movements. The neurovascular examination of his limb is unremarkable.
• What is the cause of his pain?
• How should this patient be managed acutely?
• What is the differential diagnosis in a patient with sickle cell disease?
Sickle cell anaemia is an autosomal recessive genetic disease that results from the substitution of valine for glutamic acid at position 6 of the beta-globin gene, leading to production of a defective form of haemoglobin, hemoglobin S (HbS). Deoxygenation of HbS leads to distortion of the red blood cell into the classic sickle shape. The sickle cells
are much less deformable than normal red cells and can obstruct the microcirculation.
This results in tissue hypoxia, which causes further sickling. Patients with a sickle cell crisis should be treated with high-flow oxygen, opioid analgesia and fluid resuscitation. If the precipitating factor is thought to be infective then intravenous antibiotics should be started.
Causes of sickle cell crises !
• Cold exposure
• Drug and alcohol use
• Pregnancy and stress
Limb and back pain are common presentations for sickle cell sufferers. Osteomyelitis should be considered as a differential diagnosis, although bone infarction secondary to a sickle crisis is 50 times more common. The two conditions have a similar presentation with common features:
• raised inflammatory markers (CRP, ESR and WCC).
Radiographs are of limited use in the acute phase of osteomyelitis, as bone destruction and periosteal reaction do not become evident until at least 10 days. A more sensitive investigation is a technetium bone scan which is reported to detect signs of osteomyelitis after 3 days. Magnetic resonance imaging is also useful in helping to identify abscesses,
sequestra and sinus tracts. A fine-needle bone aspirate provides a definitive diagnosis and can isolate the causative organism. The most common organism is Staphylococcus aureus. In sickle cell sufferers this remains the likely organism, but Salmonella and Enterobacter are also commonly cultured.
• Radiographical evidence of osteomyelitis may not be present during the first 10 days.
• A sickle cell crisis should be initially treated with analgesia, oxygen and fluids