Persistent Bilateral Mydriasis Associated With a Pituitary Adenoma in a Horse.
Authors: Allnoch Lisa, Peters Martin, Wiemer Frank, Wohlsein Peter
Journal: Journal of equine veterinary science
Summary
# Editorial Summary This case report documents a 23-year-old warmblood gelding presenting with progressive bilateral mydriasis and vision loss over a decade-long clinical course of pituitary pars intermedia dysfunction, ultimately confirmed as an expansile pituitary adenoma at postmortem examination. The authors performed detailed pathomorphological investigation of the cranial vault, revealing degenerative changes not only within the tumour itself but also in the preganglionic oculomotor nerve, ciliary ganglion, and optic chiasm—structural damage consistent with cavernous sinus syndrome resulting from mass effect. The persistent bilateral mydriasis and loss of pupillary light reflex distinguished this case from typical PPID presentations, highlighting how space-occupying lesions in the sellar region can cause progressive neurological complications beyond the endocrine dysfunction initially suspected. For practitioners, this case serves as a reminder that refractory or worsening clinical signs in aged horses with known pituitary disease warrant investigation beyond metabolic management, particularly when ocular abnormalities develop; the combination of bilateral mydriasis with decreased vision in an older equine patient with PPID history should prompt consideration of neoplastic transformation. Whilst pituitary adenomas are relatively uncommon in horses, their potential for significant neurological morbidity underscores the importance of long-term monitoring and recognition that medical responsiveness to dopamine agonists may plateau or decline as the disease progresses.
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Practical Takeaways
- •Bilateral mydriasis and vision loss in horses with pituitary disease warrants imaging to rule out adenoma with secondary oculomotor nerve compression.
- •Long-standing pituitary pars intermedia dysfunction can progress to neoplastic disease; chronic cases losing therapeutic response should be re-evaluated for complications.
- •Recognition of cavernous sinus syndrome features (mydriasis, decreased vision, potential involvement of CN III, IV, VI, V1, V2) in horses with pituitary disease may guide clinical decision-making regarding prognosis.
Key Findings
- •A 23-year-old horse with 10-year history of pituitary pars intermedia dysfunction developed severe bilateral mydriasis and bilateral vision loss secondary to pituitary adenoma.
- •Postmortem examination revealed degenerative changes in the preganglionic oculomotor nerve, ciliary ganglion, and optic chiasm caused by the expansile pituitary mass.
- •The ocular clinical presentation shared features characteristic of cavernous sinus syndrome, indicating involvement of multiple cranial nerves and associated structures.