Keith Hyland, PhD, details common misdiagnoses of AADC deficiency and explains what physicians should look for to differentiate AADC deficiency from other conditions
Hyland: There’s actually a broad spectrum of different misdiagnoses. Many of the kids get classified as children with seizure disorders. Many of them get diagnosed with cerebral palsy, which obviously is, in a way, it’s a bad diagnosis to get because treatment often stops if a child gets the label of cerebral palsy. Other situations have been people who have diagnosed it as having mitochondrial disease. There’s a broad spectrum of problems that have been considered before they actually get to the diagnosis for AADC deficiency.
In AADC deficiency you get something which is called oculogyric crises, which basically is where your eyeballs roll up and go to the top of your head. It’s a form of dystonia, it’s a dystonia of the eye.
Often physicians see that happening and they suspect that there’s a seizure and that seizure activity that’s causing those eyes to roll around in the head.
Now the way that you can differentiate those, the seizure disorders obviously have abnormal EEGs and in AADC deficiency, the EEG is generally normal. Also, in cerebral palsy, the MRIs are abnormal or in classical cerebral palsy, the MRIs are abnormal but in AADC deficiency, MRI changes are very minor. So, if the physician is considering a seizure disorder or cerebral palsy, if they then look at the MRIs and the EEGs, when they’re normal, they can move away from that diagnosis of a seizure disorder or cerebral palsy.
Similarly, in either seizure disorders or cerebral palsy, there aren’t really any autonomic changes. So, if the physician is thinking AADC and trying to decide whether it might be a primary seizure disorder or cerebral palsy, if they look at the autonomic problems and they’re there in that child, that will move them away from the seizure diagnosis or cerebral palsy diagnosis.
It’s quite interesting that patients with cerebral palsy kind of get a label of cerebral palsy and many of them get that label and then they don’t get any further treatment or any further investigation, which is a great shame because it’s quite likely that a fair number of those patients may have AADC deficiency. The reason I say that is that many of the patients that had been described in the literature, actually were initially diagnosed as having cerebral palsy. It’s obviously important that we find those patients, which we can do by screening using the 3-O-methyldopa assay. It’d be a simple test, it’d be easy to get into those patients and determine who of them or which of those patients have AADC deficiency.