$re = '/INTERROGATION\s*(.+?)(?:\R+\d|\R*$)/s';
$str = '1. QUESTION DE PLUSIEURS MOTS EN MAJUSCULE? réponse possible ici
2. QUESTION DE PLUSIEURS MOTS EN MAJUSCULE SANS POINT D\'INTERROGATION
réponse possible ici
4. QUESTION IDENTIQUE DE PLUSIEURS MOTS EN MAJUSCULE SANS POINT D\'INTERROGATION
réponse possible ici';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php