Isolated injury to the fourth nerve can be caused by any process that stretches or compresses the nerve. A generalized increase in intracranial pressure—hydrocephalus, pseudotumor cerebri, hemorrhage, edema—will affect the fourth nerve, but the abducens nerve (VI) is usually affected first (producing horizontal diplopia, not vertical diplopia). Infections (meningitis, herpes zoster), demyelination (multiple sclerosis), diabetic neuropathy and cavernous sinus disease can affect the fourth nerve, as can orbital tumors and Tolosa–Hunt syndrome. In general, these diseases affect other cranial nerves as well. Isolated damage to the fourth nerve is uncommon in these settings.