5th June 2025

Investigations

Initial investigations look at auto-antibodies, with over 90% of patients having a positive ANA. Within this group there are subsets of mutually exclusive antibodies, which are associated with distinct clinical pictures:

• Anti-topoisomerase I (anti-Scl70) 
  • Seen in 20% of patients
  • Associated with an increased risk of ILD and diffuse skin involvement
• Anti-RNA polymerase III antibody
  • Seen in 20% of patients
  • Associated with renal crisis
• Anti-centromere antibodies
  • Seen in 20-25% of patients
  • Associated with limited skin involvement and overall better prognosis
• In the remaining 40% no specific auto-antibody has been identified yet 

Further investigations to assess for systemic involvement are required. Pulmonary involvement can be investigated with pulmonary function tests and high-resolution CT of the lungs. Cardiac involvement requires ECG and echocardiogram (ECHO). If the ECHO finds elevated right ventricular systolic pressure, the patient should be referred for a right-heart catheterisation and full evaluation, as ECHO findings may not be indicative of the true pulmonary artery pressures. For gastrointestinal symptoms such as dysmotility and reflux, a barium swallow can be a useful test. Anaemia or melaena can indicate chronic GI blood loss from gastric antral vascular ectasia syndrome (GAVE) and required upper GI endoscopy. If inflammatory myositis develops, patients will require blood tests for serum muscle enzymes, possibly followed by a nerve conduction study and a muscle biopsy.