Differentials
Gout
SIGNS / SYMPTOMS
Presents with severe pain, swelling, and redness of the affected joint, which is often the metatarsophalangeal joint of the big toe.
Gout can be seen in patients with sickle cell disease who have associated renal disease.
INVESTIGATIONS
Joint aspiration shows needle-shaped negatively birefringent monosodium urate crystals.
Septic arthritis
SIGNS / SYMPTOMS
Typically presents with fever and swelling of the affected joint.
Suspect in sudden onset of monoarthritis.
Patients at risk include those with recent bacteraemia from pneumonia or urinary tract infection, or with history of intravenous drug use, rheumatoid arthritis, prosthetic joint, or immunocompromise.
INVESTIGATIONS
Joint aspiration will show a purulent effusion, high white blood cell count, positive Gram stain, and positive culture.
Connective tissue diseases
SIGNS / SYMPTOMS
May present with malar (butterfly) rash; photosensitivity; swollen, painful, and stiff metacarpophalangeal joints; anaemia; and vasculitis.
INVESTIGATIONS
Serological work-up may show antinuclear antibody and/or rheumatoid factor positivity.
Avascular necrosis
SIGNS / SYMPTOMS
Presents with pain typically in the hip or shoulder, and can be differentiated from a vaso-occlusive crisis by its chronicity.
INVESTIGATIONS
Magnetic resonance imaging of the affected joint would show no difference between avascular necrosis caused by sickle cell disease and necrosis caused by other aetiologies (e.g., injury or joint dislocation).
Perthes' disease
SIGNS / SYMPTOMS
Condition of childhood characterised by necrosis of femoral epiphysis. Usually seen in children 4 to 10 years of age.
May be associated with thrombophilia.[27]
INVESTIGATIONS
X-ray is diagnostic. May be difficult to distinguish from sickle cell osteonecrosis.
Acute abdomen
SIGNS / SYMPTOMS
Vaso-occlusive crises owing to small infarct of the abdominal viscera must be differentiated from other acute abdominal disorders. For example, acute cholecystitis presents with right upper quadrant pain (worse after eating fatty foods), nausea and vomiting, and a positive Murphy's sign. Meanwhile, acute pancreatitis typically presents with abdominal/epigastric pain that radiates to the back.
INVESTIGATIONS
Amylase and lipase are elevated in pancreatitis. Abdominal ultrasound in pancreatitis may show ascites, gallstones, dilated common bile duct, and an enlarged pancreas. In cholecystitis, ultrasound may show gallstones or a thickened gallbladder wall.
Osteomyelitis
SIGNS / SYMPTOMS
Painful bone episodes in sickle cell anaemia are clinically indistinguishable from those experienced in osteomyelitis.
INVESTIGATIONS
Magnetic resonance imaging bone scans do not confidently differentiate the two conditions.
Persistent pain localised to one area, especially in a febrile patient, suggests the possibility of osteomyelitis.
Blood cultures positive for Salmonella species, Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae type b, or Escherichia coli favour diagnosis of osteomyelitis.
Trauma
SIGNS / SYMPTOMS
Pain and signs of injury related to the site of trauma.
INVESTIGATIONS
If trauma is suspected in a child who cannot communicate, imaging of the affected area is helpful, along with close observation.
Parvovirus B19 infection
SIGNS / SYMPTOMS
Erythematous rash on cheeks (‘slapped cheeks’) with lacy, reticular exanthem on extremities and torso.
Patients may develop arthralgia/arthritis of the small joints of the hands, the wrists, knees or ankles. May be preceding respiratory symptoms or fever.
INVESTIGATIONS
Anaemia is accompanied by a very low reticulocyte count (<1%). IgM antibodies to parvovirus are usually present at the time of diagnosis, but may develop days after the onset of aplastic crisis.
Iron deficiency anaemia
SIGNS / SYMPTOMS
May be a history of fatigue, exertional dyspnoea, restless leg syndrome, nail changes or pica.
May be a history of overt blood loss e.g., menorrhagia, or gastrointestinal symptoms indicating a source of covert blood loss.
INVESTIGATIONS
Serum ferritin, iron and transferrin saturation decreased; total iron binding capacity increased.
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