Diagnosis using polymerase chain reaction and outcomes in herpes simplex keratitis.

Abstract

Editor, Herpes simplex keratitis (HSK) is a major cause of unilateral blindness in developed countries (Guess et al. 2007). A fast and highly sensitive test could assist in the diagnosis to guide adequate antiviral therapy. We aimed to report the use of herpes simplex virus (HSV) polymerase chain reaction (PCR) test for the diagnosis of HSK and its relationship to the outcomes in these patients over a 2-year period at the Sydney Eye Hospital, Australia. A retrospective case review of all patients who received antiviral medications for HSK was conducted. Cases were identified from HSV PCR swab results, pharmacy records and hospital coding data from 2012 to 2013. Clinical details were collated from the medical records. Herpes simplex virus type 1 and type 2 were detected using the HSV-1 HSV-2 VZV R-gene® kit, a real-time PCR on DNA extracted from human clinical samples (Argene, bioMérieux SA, Marcy-l'Etoile, France) according to manufacturer’s instructions. The tests were performed using a Roche LC480 thermal cycler for real-time amplification. The R-gene kit’s sensitivity ranged between 91% and 100% and specificity 95% and 100% depending on the study (Biomerieux 2016). Patients were sub-grouped depending on the clinical features: epithelial, stromal with ulceration (SHSK+U), stromal without ulceration (SHSK−U), endothelial, keratouveitis and active HSK with prior corneal graft. Outcome was determined when the initial antiviral therapy was stopped or changed and classified as clinically improved or worsened. Two hundred and fifty-two patients were included with HSV PCR performed in 166 (66%) at presentation. The HSV-1 PCR test was positive in 32/94 (34%) patients with epithelial HSK, 4/14 (29%) patients with SHSK+U, 3/11 (27%) patients with active HSK and corneal graft, and 6/33 (18%) patients with keratouveitis. Overall, the positivity rate was 27% (45/166). Of the patients with prior corneal graft, two were diagnosed with epithelial HSK and one with SHSK+U. A clinically improved or worsened outcome was determined for 112 of 166 patients (67%) tested with HSV PCR (Table 1). There was no statistical association between the type of outcome and HSV PCR result (p = 0.5). Polymerase chain reaction test has been reported as a highly sensitive diagnostic test for HSK (Subhan et al. 2004; Azher et al. 2017). Its diagnostic power varies depending on the type of HSK, previous acyclovir therapy, use of topical anaesthetics or dyes, and viral load in the specimen (Shoji et al. 2016). The PCR test most likely identifies patients with a dendritic ulcer as it is a manifestation of active viral infection (Azher et al. 2017). Consequently, clinicians requested the test to patients with a presence of a epithelial defect and provisional diagnosis of epithelial HSK [94/123, (76%)], SHSK+U [14/19, (74%)], keratouveitis [33/49, (67%)] or active HSK with corneal graft [11/25, (44%)]. Stromal HSK is thought to occur due to an immune response to the virus rather than via viral infection (Azher et al. 2017). It is also assumed that stromal and endothelial HSK are recurrent episodes (Guess et al. 2007) and the patients may have a previous positive PCR result. Due to the absence of an epithelial defect, it is not possible to access the stroma and therefore to obtain a sample of the area affected. This may explain the negative PCR results for this type of HSK (Azher et al. 2017). This may also be the reason why clinicians did not request as many PCR tests on patients with SHSK−U [11/22, (50%)] and endothelial HSK [3/14, (21%)] compared with the epithelial HSK (76%) and SHSK+U (74%) groups. The positivity rate for both, SHSK−U and endothelial HSK, was 0% supporting the above hypothesis. In conclusion, the HSV PCR test had an overall low positive rate. Regardless of the PCR result, most patients improved with the initial antiviral therapy, especially for epithelial HSK. A clinical diagnosis of HSK may therefore be sufficient to guide treatment.