Primary Vitreoretinal Lymphomas: A Diagnostic Challenge - Report of Two Recent Cases with Retinal Biopsies and Molecular Investigations in Halifax, Nova Scotia.

Introduction: Primary vitreoretinal lymphomas (PVRL) are a type of central nervous system lymphoma that arise in the retina, vitreous, or optic nerve without initial brain involvement. The clinical diagnosis can be a challenge since the disease mimics uveoretinitis in its presentation and initial treatment response to steroids. Diagnostic confirmation with vitreous cytology has been the gold standard for diagnosis. However, there are limitations of vitreous cytology, such as low volume of sample, low number of lymphoma cells within the sample, and poor preservation of cells due to shearing forces of vitrectomy. There has been a long-standing need for alternative options to improve the diagnostic yield of PVRLs. Recently, MYD88 gene mutations (myeloid differentiation response gene 88) have been found in 69-82.4% of PVRLs. Case Presentations: Case 1: a 89-year-old male presented with a retinal detachment post cataract surgery. He had subsequent surgical repair but continued to have poor and worsening vision and developed constitutional symptoms, including weight loss and decreased appetite. A vitreous sample submitted for molecular studies demonstrated the MYD88 L265P mutation, and a retinal biopsy showed large B lymphocytes infiltrating the retina. Case 2: a 62-year-old female was referred to the Uveitis Clinic for assessment of chronic right eye panuveitis and left eye anterior uveitis. The patient developed symptoms (blurry vision and photophobia) 9 months prior to the referral. A vitreous biopsy was conducted and was negative for MYD88 mutations, and large B cells were not seen on vitreous cytology. The fundus view post-vitrectomy revealed an area of necrotizing retinitis. The patient was started on empiric treatment for herpetic and parasitic etiologies and on high-dose oral prednisone shortly after. She had a further decline in her right eye vision with significant extension of the necrotizing retinitis into the macula and optic disc. A retinal biopsy then revealed atypical large B cells infiltrating the retina. Conclusion: PVRLs are rare, and establishing the diagnosis is difficult. The traditional use of vitreous cytology has its limitations. Recent molecular advances, in particular the detection of MYD88 mutation, are extremely helpful in confirming the diagnosis, but in certain cases, retinal biopsies may still be required.