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The differential diagnosis of retinitis associated with panuveitis includes:

• Bacterial endophthalmitis
  
• Toxoplasma chorioretinitis
  
• Acute retinal necrosis (HSV, VZV)
  
• CMV retinitis (not usually associated with vitritis)
  
• Syphilis
  
• Sarcoidosis
  
• Tuberculosis
  
• Behcet’s disease
  
• Lymphoma

The patient was otherwise healthy with no significant past history. He was immediately referred to hospital for a vitreous biopsy. PCR testing was positive for Herpes Simplex Virus-1 (HSV-1). Other blood tests were normal.

The patient was admitted to hospital and received repeat intravitreal injections of the anti-viral Foscarnet over a one week period. He received intra-venous administration of the antiviral acyclovir. Oral steroids were commenced after a week. There was steady improvement in the retinitis and vitritis and the patient was discharged 10 days later on oral antiviral agents and a tapering course of oral steroid. He is currently being monitored closely for the possible development of retinal detachment.

Acute retinal necrosis (ARN) is a typically unilateral panuveitis characterised by one or more foci of retinal necrosis with discrete borders. There is usually significant associated anterior uveitis and vitritis, and often occlusive retinal arteritis. Without treatment the retinal lesions progress rapidly, and there is often bilateral involvement and significant visual morbidity.

While varicella zoster virus (VZV) or one of the herpes simplex viruses (HSV-1 or HSV-2) is most often the cause of ARN, cytomegalovirus (CMV) occasionally causes the condition.(1) In addition, rare cases of Epstein-Barr virus-associated retinitis and panuveitis have occurred.

Acute retinal necrosis syndrome is uncommon. Two recently published nationwide surveys from the United Kingdom estimated the incidence of ARN at one case per 2 million people per year.(2,3) It typically presents with eye redness, periorbital pain, photophobia, and vision loss. Anterior-segment findings include episcleritis, scleritis, keratitis, and/or anterior chamber inflammation, which may be either nongranulomatous or granulomatous.

Posterior-segment findings include vitreous inflammation, one or more areas of full-thickness necrotizing retinitis, and occlusive arteritis. Signs of optic neuropathy may be present when the optic disc is involved. In approximately one-third of patients, the fellow eye may become involved, typically within six weeks of initial presentation.(4)

The wider availability of polymerase chain reaction (PCR) testing of vitreous fluid has greatly assisted diagnosis.(5) Such testing is highly sensitive for the detection of viral DNA even in small volume vitreous samples, although sensitivity can fall dramatically if antiviral therapy has already been initiated.

Intravitreal and systemic antiviral therapy forms the mainstay of treatment. Foscarnet is the preferred intravitreal agent due to its broad spectrum of viral coverage and low incidence of viral resistance, whilst systemic treatment can be given in the form of intravenous acyclovir (requiring hospital admission), or oral valacyclovir.(6) There is typically a prompt response to treatment and systemic steroid may be added later to assist with resolution of the associated vitritis. Oral antiviral treatment is usually continued for at least 3 months.(7)

Some clinicians advocate for the use of prophylactic laser photocoagulation around the area of retinitis, in order to reduce the risk of retinal detachment. However this remains controversial and there is no conclusive evidence supporting its use(8).

Retinal detachment can occur in up to three quarters of patients and presents a significant management challenge and threat to vision.(1) There is often both a rhegmatogenous component, due to retinal necrosis, and a tractional component. Long acting gas or silicone oil tamponade may be required.