Neuroretinitis is defined as a type of optic neuropathy characterized by an acute visual loss with optic disc swelling, accompanied by hard exudates characteristically arranged in a star shape around the fovea. We described a case of ocular CSD in its most common form, which is neuroretinitis. There was no feline exposure, but there was a dog bite instead. Cats are well known to be the primary host for Bartonella Henselae, in which the infected cats have asymptomatic bacteraemia lasting for months7. However, the name Cat Scratch Disease may serve as a misnomer as not only cats carry B.Hensalae. Fleas, ticks and lices has been identified as vectors for the transmission of B.Hensalae from feline to other animals8. As B.Hensalae, the causative microorganism of CSD is difficult to culture, clinical diagnosis of CSD is most often made following history of cat exposure, physical examination and confirmed with serologic test with high titres of immunoglobulin G to B. Henselae. Although majority of CSD patients has history of contact with cat, there has been increasing documented cases of ocular CSD without prior contact with cat or known vectors10,11,12.
Serology confirmed Bartonella-associated neuroretinitis has been reported following contact with other domestic animals. Our literature search yielded 9 articles with a total of 17 eyes that contracted neuroretinitis without feline exposure (Table 1). Including our patient, 6 out of the 13 (46%) patients had recent history of contact with dog prior to onset of the symptoms, while the others involved bites from guinea pig, ferret, raccoon, bull ant and tick, as well as exposure to hedgehog. These recent findings implicate that dogs and other non-feline domestic animals can be the reservoir of B. Henselae, with blood-sucking arthropods as vectors. It is known that Bartonella species has excellent specific adaptation strategies to its preferred hosts as well as survival in the vector feces13 .
It is also important to note that cross reactivity in serology testing has been observed between different Bartonella species; B. Henselae with B.Grahamii14 as well as B. Quintana15,16, both of which were reported to cause neuroretinitis. Interestingly, a case of B. Elizabethae neuroretinitis was also reported following raccoon bite17 .
Prodromal illness of fever, malaise and headache is only present in 7 out of 13 patients, while lymphadenopathy is even less. Our patient’s systemic examination did not reveal any lymphadenopathy, which is the hallmark of systemic CSD, as it only occurs in 20% of ocular CSD cases18,19. In spite of this, the finding of regional lymphadenopathy in neuroretinitis patients serves as an important clue for the diagnosis of CSD.
Bartonella-associated neuroretinitis may be unilateral or bilateral in either immunocompromised or immunocompetent patient19. Our patient presented with the typical unilateral neuroretinitis with right eye optic disc swelling, optic nerve dysfunction, subretinal fluid at macula with macula star emerging two weeks later. Habot-Wilner et al reported 90% of ocular CSD patients had optic disc swelling upon presentation, whereby 80% of this is due to neuroretinitis and the rest is diagnosed as inflammatory disc oedema18.
Apart from neuroretinitis, our patient showed presence of vessels sheathing, with involvement of veins more than arteries. He had occlusive vasculitis with a large area of capillary non-perfusion superotemporally. Around 7% of reported ocular CSD cases manifested as retinal vessel occlusions18,20,21, where it was observed that retinal arteries were more commonly involved than veins18,20. Presence of retinal vasculitis is even less frequently reported21. However, this is not a surprise as Bartonella has been shown to interact and invade endothelium, thus may elicit obliterative vasculitis23. Thus, it is also reasonable to consider CSD in cases of retinal vessel occlusion in patients lacking of known vascular risk factors.
The visual evoked potential (VEP) of our patient at two months following his initial presentation was abnormal, in which his right eye P100 latency was prolonged, signifying a conduction defect in the optic nerve. His optic nerve function remained impaired, as expected that some degree of optic neuropathy will remain even after resolution of neuroretinitis19. This can be explained by the pathogenesis of neuroretinitis as it is associated with direct involvement of the optic nerve head fibers as the primary target24 by infectious or inflammatory processes, leading to edema and fluid exudation from the inflamed cellular area of the peripapillary retina25. Therefore in bartonella neuroretinitis, the VEP will be abnormal with prolongation of latency of P100 wave and a decrease in the amplitude. However, electroretinogram (ERG) will be normal8, as the functional integrity of the retinal layers are not disrupted.
As a self-limiting disorder, the treatment of ocular cat scratch disease has been slightly controversial. Reed et al concluded that the use doxycycline and rifampicin shorten course of disease and hasten visual recovery19. This is consistent with recommendation from Fairbanks et al for a four to six weeks regimen of doxycycline or azithromycin alongside rifampicin in patients who suffer severe vision loss and/or moderate to severe systemic symptoms26. However Solley et al found no difference in the final visual outcome between treated and untreated ocular CSD20. Habot-Wilner suggested following closely patients with ocular CSD that retained their good vision upon presentation, without initiation of systemic antibiotic. However they recommended a combination of systemic corticosteroid and antibiotic for moderate to severe visual loss18. The use of corticosteroid therapy remains constroversial in infectious neuroretinitis cases. Chrousus et al reported systemic corticosteroids with or without systemic antibiotics to be effective in this condition27. The use of azithromycin has been shown to be efficacious in a prospective randomized placebo-controlled trial by Bass et al27 and Ives et al28. Both our patients showed dramatic recovery upon commencement of azithromycin. Other options would include erythromycin, doxycycline, rifampicin, ciprofloxacin and aminoglycosides30 .