At present, there are no specific laboratory changes to diagnose CVS, and the diagnosis depends on fulfilling key historical criteria (Table
Table 20.5 Diagnostic criteria (from the First International Symposium on Cyclic Vomiting Syndrome)
> 3 recurrent, severe, discrete episodes of vomiting
Varying intervals of normal or baseline health between episodes
Duration of episodes from hours to days
No apparent cause for vomiting (negative laboratory, radiographic and endoscopic testing) Supportive criteria
Stereotypical episodes are similar in regards to time of onset, intensity, duration, frequency and associated symptoms and signs
Self-limited in that episodes will resolve if left untreated Associated symptoms and signs
20.5). In the absence of positive laboratory findings, most of the testing with recurrent vomiting is directed towards excluding other treatable causes. Potentially treatable underlying gastrointestinal, neurological, renal, metabolic and endocrine causes are not rare, and are found in 12% of those who present with a cyclic pattern of vomiting. In addition, 12% (many overlapping) have an identifiable surgical disorder.2 The challenge is to determine what and how much testing should be done, because a 'shot-gun' approach can be costly, time-consuming and invasive. We conducted a cost-decision analysis and concluded that an upper gastrointestinal tract X-ray with a small bowel follow-through followed by 2 months of empiric anti-migraine therapy was the most cost-effective initial treatment strategy for CVS.12 If no therapeutic response occurs, more systematic testing should be performed (Figure 20.2).
The first step is to identify a recurrent pattern versus a single acute vomiting illness typical of gastroenteritis. The next is to distinguish between a low-grade, nearly daily chronic and explosive, intermittent cyclic pattern of vomiting. Once identified, the diagnostic evaluation involves evaluation for both gastrointestinal and non-gastrointestinal causes. In our experience, the most potentially devastating causes are sought including anatomic anomalies of the gastrointestinal tract and renal hydronephrosis by upper gastrointestinal series with small bowel follow-through and renal ultrasound examination, respectively. Metabolic and endocrine testing must be performed before intravenous glucose and fluids are administered, because these can alter respective findings on metabolic screening and evaluation of the HPA axis metabolites. The endoscopy and the head magnetic resonance imaging (MRI) are reserved for those in whom therapy has failed or who have specific symptoms suggesting peptic or allergic gastrointestinal disease or intractable headaches, respectively. Laboratory testing and a proposed algorithm for evaluation are presented in Figure 20.2.
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