QOTW – Would a CT Scan help with a definitive diagnosis of HAE with normal C1?

Oct 19, 2015

‘I am working on getting a CT scan (as requested by my physician). I’ve been told it may help in regards to a possible definitive diagnosis of HAE with normal C1. Is there truth to this and what exactly does a CT scan show during an attack?’

Dr. C:It was wonderful to see everyone at the ‘HAEA Patient Summit in Denver’. As usual, many excellent questions without enough time to answer them all. We saved the cards—this is one of the ‘unanswered questions’.

Making the diagnosis of HAE-nl-C1INH can be very challenging. As many of you are aware with the exception of the factor XII mutation we do not have a laboratory test which provides a clear confirmation of the disease. Physicians often struggle to arrive at the diagnosis mainly by piecing together supportive clinical evidence. Abdominal attacks are more frequent in type I or type II HAE compared to HAE-nl-C1INH; however, they do occur in all forms of HAE. Self-limiting recurrent abdominal pain lasting more than 6 hours is one of the clinical criteria for suspecting HAE. Requesting a CT scan during an abdominal attack can help the physician determine whether the abdominal symptoms may be due to angioedema or not. Bruce or Marc, any comments?

Dr. R:Abdominal pain is a challenging symptom to evaluate, as there are literally dozens of conditions that can be causative. It’s important to consider HAE as a possible diagnosis in these settings. C1INH testing should be done to identify or exclude HAE types 1 and 2. Unfortunately, we don’t currently have a good diagnostic test for HAE with normal C1INH, so this becomes a “diagnosis of exclusion”, meaning it’s necessary to rule-out other reasonable causes of the symptoms.

Dr. Z:During an active abdominal attack in a patient with HAE, we would expect to see fluid distending the bowel wall (at times to the point of bowel obstruction) on the CT scan. In addition, there is often free fluid in the peritoneal cavity. This occurs because of the vascular leak resulting from the generation of bradykinin, which appears to be the culprit for HAE-nl-C1INH as well as for types I & II HAE.

Dr. C:A case report in Gastroenterology in 2011 was an excellent example of using the finding on a CT scan to help arrive at a diagnosis of HAE-nl-C1inh. Any further thoughts about the use of the CT scan to assist in arriving at a diagnosis?

Dr. Z:Since we cannot “see” the swelling during an abdominal attack, the CT scan can be very helpful in telling us whether the abdominal symptoms are likely to be due to angioedema or not. Like any test, however, it is not perfect and needs to be interpreted within the full context of the clinical situation.

Dr. R:However, the sensitivity and specificity of such imaging for bowel angioedema isn’t known as we don’t have studies to definitively show how accurate such testing is in the setting of a hereditary angioedema attack. So I would view this plan as a rational but not definitive way to try to sort out the issue. In my opinion, it’s important not to develop “tunnel vision” with abdominal pain, particularly if C1INH testing is normal, but rather to ensure a comprehensive evaluation of potential causes is pursued.

Dr. C:Thank you, Bruce and Marc. We hope that continued careful gathering of information and analysis will lead to more refined answers in the future. The need to do CT scans should decrease considerably once we have a reliable biomarker to identify HAE-nl-C1INH. We look forward to our next ‘Question of the Week’.

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