@jixster @charlotte61 here is a reference to that 20%

: Giant cell arteritis: reviewing the advancing diagnostics and
management Eye; https://doi.org/10.1038/s41433-023-02433-y

CLINICAL PRESENTATION
GCA has heterogeneous clinical features due to the overlapping spectrum of the known clinical phenotypes: cranial GCA (C-GCA), large vessel GCA (LV-GCA), and polymyalgia rheumatica (PMR) (Fig. 2) [42]. The majority of people with cranial GCA will have symptoms of new onset headache, jaw claudication and cutaneous allodynia [8, 43, 44]. Nearly half of people with GCA have symptoms of PMR (Fig. 2) while up to one-fifth of people with PMR will be diagnosed with GCA [5, 42].