Validation of ICD codes for the identification of patients with functional seizures

To evaluate the validity of ICD-9-CM and ICD-10 codes for the identification of patients with functional seizures (FS).

We evaluated the charts of 800 patients including 400 in an institution wide sample and 400 in an epilepsy monitoring unit (EMU) sample. Half of the patients from each sample came from 2012-2013 and 2022-2023 since ICD-9-CM codes and ICD-10 codes were exclusively used in these respective periods. The charts of each patient were manually reviewed and evaluated for the presence of epilepsy and FS. Based on the 2013 International League Against Epilepsy (ILAE) Nonepileptic Seizures Task Force guidelines we determined whether a patient had either presumptive (clinically established or documented) or probable/possible FS. We evaluated ICD-9-CM codes 300.11 (conversion disorder) and 780.39 (other convulsions) as well as ICD-10 codes F44.5 (conversion disorder or functional neurological disorder with seizures or convulsions) and R56.9 (unspecified convulsions). The positive predictive value (PPV) of each ICD code was calculated in the institution wide sample and the sensitivity, specificity, PPV and negative predictive values (NPV) were calculated in the EMU sample.

In the institution wide sample, F44.5 had a PPV of 74.0 % (64.6-81.6) for presumptive FS and 80.0 % (71.1-86.7) when probable/possible FS patients were included. The code 300.11 had a PPV of 52.0 % (42.3-61.5) for presumptive FS and 59.0 % (49.2-68.1) when probable/possible FS patients were included. Codes R56.9 and 780.39 had PPVs that were equal to or less than 20 %. In the EMU sample, the code F44.5 had a sensitivity, specificity, PPV and NPV of 67.1 % (56.3-76.3), 95.8 % (90.5-98.2), 91.7 % (81.9-96.4), and 80.7 % (73.4-86.4), respectively for presumptive FS. The code 300.11 had a sensitivity, specificity, PPV and NPV of 30.1 % (20.8-41.4), 95.3 % (90.1-97.8), 78.6 % (60.5-89.8), and 70.4 % (63.1-76.7), respectively for presumptive FS. The codes R56.9 and 780.39 performed poorly.

ICD codes had a mixed performance when used to identify patients with FS. ICD-10 code F44.5 appeared to perform the best overall.