How does muscle weakness from glucocorticoids differ from that from vita d deficiency and that from serotonin toxicity?

Weakness.: Weakness is weakness no matter the cause. That said, steroids can in some instances cause weakness via damage to type 2 muscle fibers (those that produce power). Vit d def also causes atrophy of type 2 muscle fibers which tends to be more reversible (with vit d replacement). Serotonin toxicity causes uncontrolled muscle spasms which, if severe, can cause severe muscle breakdown (type 1 & 2 fibers).