Is paraneoplastic syndrome a mets, cancer like spread from the lung to elsewhere an is it always seen in cat scan ?

Not metastases: Paraneoplastic syndromes result either from substances produced by a tumor (perhaps a pituitary adenoma making prolactin and causing impotence) or from the immune response against a tumor attacking healthy cells (perhaps the attack on an oat cell lung cancer causing blindness). They have nothing to do with whether the tumor has metastasized.