Case Report and Literature Review: Isolated Trochlear Nerve Palsy due to Herpes Zoster Infection.

INTRODUCTION: Trochlear nerve palsy (TNP) is a common cause of vertical diplopia resulting from superior oblique muscle weakness. While herpes zoster is a well-documented cause of cranial neuropathies, reports of TNP associated with herpes zoster infection remain limited.

CASE PRESENTATION: We report a case of a 65-year-old patient with typical herpes zoster ophthalmicus on the left side of his face with subsequent corneal endotheliitis and isolated TNP. The MRI revealed a faint enhancement at the cavernous sinus on the same side as the TNP. Cerebrospinal fluid detected human herpesvirus 3, confirming the diagnosis. An intravenous antiviral was administered for 14 days with prolonged maintenance to prevent recurrence. Oral corticosteroids were also used as an adjuvant to reduce inflammation. After treatment, the uveitis subsided, and the vertical diplopia recovered partially. TNP from herpes zoster is a rare presentation. The underlying pathogenic mechanisms, including potential direct viral invasion, inflammatory responses, and possible vasculopathy affecting the trochlear nerve, are explored.

CONCLUSION: TNP can be a rare neuro-ophthalmic complication of herpes zoster infection. Clinicians should maintain a high index of suspicion when assessing patients with cranial neuropathies in the context of herpes zoster. Prompt antiviral therapy and supportive measures can aid in the resolution of symptoms and alleviate potential long-term sequelae.