The vast majority (87%) of patients with CVS have a migraine association either based most commonly on a family history of migraine or, less frequently, on the subsequent development of migraines in the affected child. Because these associated symptoms occurred less than half the time, we did not use headache, photophobia and phonophobia as specific criteria to determine who had migraine-associated CVS. When we examined the remainder with non-migraine-associated CVS (13%), they appeared to have longer episodes, had more emeses per episode and were far less likely to respond to anti-migraine therapy (79 vs. 36%).5 At present, we cannot determine whether the non-migraine CVS is pathophysiologically distinct or simply resides at the severe end of the same mechanistic spectrum.
Are there more subtypes of CVS? Although we have been able to differentiate other subgroups based on precipitating events, clinical pattern and associated symptomatology, there are too few subjects in each to know whether there are significant differences. In Sato's subtype, described patients have hypertension and profound lethargy to the point of inability to walk, talk or respond. We have found that these patients generally have more prolonged episodes (102h vs. 50h) and increased vomiting per episode (75 vs. 31 emeses).
Several children with developmental and growth delay, seizures and mild lactic acidosis are suspected of having underlying mitochondrial enzymopathy from a mtDNA mutation. Indeed, nine patients with this clinical picture have been found to have mutations in the D-loop or control region of the mtDNA.36 Others with CVS have been found to a have either a large rearrangement or a single point mutation (MELAS).16,24
There are several other clinical patterns that can be identified. Again, it is unclear whether they simply represent various inciting stimuli that initiate the same pathophysiological cascade, or whether they represent distinct effector pathways. We hope that delineation of clinical patterns into subgroups may ultimately point us towards potential treatment approaches. For instance, some appear to have episodes that occur after periods of fasting, often induced by illness. They appear to respond rapidly to intravenous glucose and are suspected of being heterozygote carriers of disorders of fatty acid oxidation. Others have a stable periodicity (e.g. 60 days) to their episodes independent of stress or infectious triggers. Stable periodicity has been observed in some postmenarchal girls who have episodes at the onset of their menses and often respond to birth control pills with a low estrogen dose.2 Some respond to pro-kinetic agents, but because of the lack of motility studies, it is not known whether they have documented gastric dysmotility.37 Finally, in a group of children, dietary triggers of their episodes can be identified. Some are initiated by typical migraine precipitants including cheese, chocolate and monosodium glutamate, whereas others are triggered by food allergies identified by RAST
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