Twenty percent (122/597) of patients with only the ICD-9-CM diagnosis of PTH received two headache diagnoses in ICD-10-CM (Fig 1, Panel C), with headache NOS and migraine diagnoses added to the PTH code for about 5% (31/597) and 4% (25/597) patients, respectively (Table 2, Panel C). Here, PTH is linked to migraine disorder.