BACKGROUND: The diagnosis of nonconvulsive status epilepticus (NCSE) can pose a 
challenge. Electroencephalogram (EEG) patterns can be difficult to interpret, 
and the absence of an EEG correlate does not rule out the diagnosis of NCSE. In 
this setting, neuroimaging tools to help in the diagnosis are crucial. Our aim 
was to evaluate the role of 99mTc-hexamethyl propyleneamine oxime (HMPAO) single 
photon emission computed tomography (SPECT) and quantitative HMPAO-SPECT 
(QtSPECT) in patients with clinical suspicion of NCSE, and to evaluate their 
value in the final diagnosis of NCSE.
METHODS: We recruited consecutive patients admitted in our center with suspicion 
of NCSE, and selected those who underwent an HMPAO-SPECT. All patients were 
admitted to the neurology ward and underwent an EEG. We divided the patients 
into those who were finally with diagnosed NCSE (NCSE-p) and those who were not 
(non-NCSE) according to the Salzburg Diagnostic EEG criteria. Sensitivity and 
specificity of the diagnostic tools were calculated. The SPECTs were acquired in 
a Skylight SPECT (Philips Healthcare, Amsterdam). The injections were done 
during the clinical episode suspected of being an NCSE. The HMPAO-SPECT was 
analyzed by two experts and was also quantified. All data were normalized to the 
SPM SPECT template. We used an external healthy normal database to obtain a 
Z-score map for each individual versus the normal database. The Z-score maximum 
(Zmax) was extracted from each region of the AAL atlas as was the percentage of 
voxels with a Z-score higher than 2.5 (N(%)). A logistic regression combining 
the Zmax, N(%), and the effect of patient age was fitted to predict the final 
NCSE diagnosis. A receiver operator characteristic (ROC) curve and the area 
under the curve (AUC) were obtained to evaluate the classification performance.
RESULTS: We included 55 patients, 21 of them women (38.9%), with a median age of 
62.1 years old (range 25-84). Thirty-six patients were with diagnosed NCSE 
(62.9%). Initial EEG had a sensitivity of 61.1% and a specificity of 89%. Most 
of the patients were critically ill with diagnostic difficulties, and it could 
be one of the main reasons to find low sensitivity of the Salzburg diagnostic 
EEG criteria. The Zmax and N(%) were significantly higher in NCSE-p than in 
non-NCSE (p = 0.005 and p < 0.001, respectively). The HMPAO-SPECT qualitative 
analysis had a sensitivity of 80.5% and specificity of 89.5% while QtSPECT had a 
sensitivity of 82% and specificity of 81%.
CONCLUSION: Both 99mTc-HMPAO-SPECT and QtSPECT can be useful in the diagnosis of 
NCSE. This article is part of the Special Issue "Proceedings of the 7th 
London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".