Diagnosis: Tentative diagnosis is unilateral anterior uveitis based on the classic ophthalmic exam findings of a painful, red, cloudy eye with miosis and aqueous flare. The systemic signs (fever, lethargy) and lab abnormalities (thrombocytopenia, hyperglobulinemia) strongly suggest an underlying systemic, likely infectious, cause.
DDx:
For the red eye: The primary differentials include glaucoma and a deep corneal ulcer with reflex uveitis.
For the underlying cause of uveitis: Given the signalment and history (hunting dog, rural area) and the finding of thrombocytopenia, tick-borne infectious diseases (e.g., Ehrlichia canis, Rocky Mountain Spotted Fever) are high on the list. Other considerations include systemic fungal infections (e.g., Blastomycosis), protozoal infections, neoplasia (e.g., lymphoma), and immune-mediated disease.
Diagnostic tests:
Ophthalmic diagnostics:
Intraocular Pressure (IOP) measurement (Tonometry): To differentiate from glaucoma. Uveitis typically causes a low IOP.
Result in this case: OS = 8 mmHg, OD = 17 mmHg [Ref: 15-25 mmHg]. This low pressure in the affected eye supports the diagnosis of uveitis. Fluorescein stain: To rule out a corneal ulcer before starting topical steroids.
The stain was negative in this case.
Systemic diagnostics:
Infectious Disease Panel: A blood sample was submitted for a 4Dx Plus SNAP test and tick-borne disease PCR panel. The 4Dx test was positive for Ehrlichia canis antigen.
Thoracic Radiographs: Three-view chest x-rays were performed to screen for fungal disease or metastatic neoplasia, which were unremarkable.
Definitive diagnosis: Anterior uveitis secondary to systemic Ehrlichia canis infection.
Treatment: The treatment plan is twofold: control the ocular inflammation to preserve vision and treat the underlying systemic infection.
Ocular Treatment:
Topical anti-inflammatory: Prednisolone acetate 1% ophthalmic suspension, 1 drop in the left eye every 6 hours to control the inflammation.
Topical mydriatic/cycloplegic: Atropine 1% ophthalmic ointment, a small strip applied to the left eye every 12 hours. This dilates the pupil to relieve the pain from ciliary muscle spasms and to prevent the iris from scarring down to the lens (posterior synechiae).
Systemic Treatment:
Antibiotic: The dog was started on Doxycycline at 10 mg/kg orally once daily for 28 days to treat the Ehrlichia infection.
Systemic anti-inflammatory: A short, anti-inflammatory course of a systemic NSAID (e.g., Carprofen) was considered for the fever and discomfort but held in reserve to monitor initial response.
Monitoring: The patient will be re-evaluated in 3-5 days to check the intraocular pressure and assess the response of the uveitis to topical therapy. The atropine frequency will be reduced as the pupil remains dilated, and the prednisolone will be tapered slowly over several weeks based on clinical response. The dog's platelet count and clinical signs will be monitored for response to the doxycycline.
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