Laboratory Studies
Perform hematology tests, a sepsis screen, and metabolic (profile) tests.
Plecko et al have confirmed pipecolic acid (PA) levels are elevated in the plasma of patients with pyridoxine (vitamin B-6)–dependent seizure (PDS) both before and after treatment with pyridoxine. [16] Furthermore, alpha amino adipic semialdehyde (AASA) levels are also elevated in plasma, urine, and cerebrospinal fluid (CSF). [26] They have recommended PA and AASA levels in plasma and urine be used as markers to select for patients who need molecular analysis of the antiquitin gene. [18]
Imaging Studies
Despite several reports about imaging studies, no typical abnormality has been found in PDS. [1, 2]
A high prevalence of structural CNS defects has been reported, as well as varying degrees of grey and white matter atrophy, thinning of the corpus callosum, and the presence of mega cisterna magna. [1]
Progressive cortical-white matter atrophy and ventricular dilation is also present in inadequately treated patients with PDS. [1, 2]
Hydrocephalus of unknown origin can also occur.
Baxter reports apparent cysts adjacent to the lateral ventricles in some neonatal-onset ultrasonographic images.
CT scanning and MRI reveal structural abnormalities in the brain in addition to white matter abnormalities. [2]
CT scanning and MRI do not have a well-established role in the diagnosis of PDS. [1]
Other Tests
Following pyridoxine administration, the EEG usually takes 2-6 minutes to normalize. The pattern is typically suggestive of diffuse and focal dysfunction and may show focal discharges; however, some EEG patterns have been normal (ie, bursts or runs of high-voltage, relatively bilateral synchronous sharp and slow [1-4 Hz] wave activity [either ictally or interictally]). [1]
EEG does not have a well-established role in the diagnosis of PDS. One report suggests that the abnormal EEG is a result of the administration of anticonvulsants to the patient prior to the diagnosis of PDS. [21]
Two case studies by Cirillo et al present the difficulties in diagnosing pyridoxine-dependent seizures by using EEG response to pyridoxine treatment. One patient who was later diagnosed with PDS had no EEG changes while another patient who had extreme EEG changes was not diagnosed with PDS. The study recommended the continuation of oral pyridoxine treatment until laboratory testing confirms the diagnosis. [27]
Perform a CSF examination (ie, lumbar puncture).
