Hallmarks of primary headache: part 4 – rare headache syndromes. - Sebastianelli, Gabriele; Ha, Woo-Seok; Messina, Roberta; Pan, Li-Ling Hope; Labastida-Ramirez, Alejandro; Rubio-Beltran, Eloisa; Vuralli, Doga; Wells-Gatnik, William; Yener, Sophie Merve; Martelletti, Paolo (Journal of Headache & Pain, 2026)