Visual loss after cat scratch

Visual loss associated with neuroretinitis (optic disc swelling with a macular star) should prompt questions about contact with cats.

CASE HISTORY

A man aged 25 attended the eye casualty clinic after three days of gradually deteriorating visual acuity in the right eye. For the previous two weeks he had experienced flu-like symptoms from which he was now recovering. He owned a kitten which had scratched him on numerous occasions over the past few weeks.

Best corrected visual acuities were 6/18 in the right eye and 6/4 in the left eye. There was no relative afferent pupillary defect and colour vision was normal. Fundoscopy revealed a right swollen optic disc, macular exudates in a star formation and some superficial retinal haemorrhages (Figure 1). There was no other sign of inflammation in the right eye and the left eye appeared normal. Fluorescein angiography showed some late leakage from the right disc. Full blood count, urea, electrolytes, erythrocyte sedimentation rate, serum angiotensin converting factor, cytomegalovirus serology, chest X-ray and CT of the brain and orbits were all either normal or negative. However, immunofluorescent antibody titres to Bartonella henselae were 1:80 for IgM and 1:4256 for IgG, both indicative of current or recent cat-scratch disease. His right visual acuity subsequently deteriorated to 6/60 and a relative afferent pupillary defect developed with some loss of colour vision. After a course of ciprofloxacin vision improved to 6/6; the fundus appearance and colour vision became normal and the pupillary defect resolved.

Figure 1.

Fundus of right eye showing neuroretinitis—i.e. disc swelling and macular exudates (arrows)—and superficial retinal haemorrhages in the inferonasal retina

COMMENT

The usual reservoir for B. henselae is cats, among which the transmission vector is the cat flea, Ctenocephalides felis.¹ In the UK, positive serology is found in about 40% of cats, whether tame or feral, but only 3% of pet dogs.² In a person infected by a cat scratch or bite a local mild infection is followed by regional lymphadenopathy, low-grade fever and malaise. In a minority of patients extranodal dissemination can lead to the broad range of clinical manifestations summarized in Box 1.^1,3

Box 1.

Clinical manifestations of cat-scratch disease

Ocular	Non-ocular
Parinaud's oculoglandular	Polyneuritis
syndrome	Arthritis
Disciform keratitis	Erythema nodosum
Anterior uveitis	Hepatosplenic infections
Vitritis	Encephalopathy
Pars planitis	Osteomyelitis
Focal retinal vasculitis	Endocarditis
Neuroretinitis
Retinal vascular occlusions
Focal choroiditis
Serous retinal detachment
Peripapillary angiomatous lesions

Whether immunocompetent individuals with ocular cat-scratch disease need treatment is debatable since the natural progression is for complete recovery within a few months. However, systemic antibiotics do seem to shorten disease duration and speed visual recovery.⁴ Alternatives to ciprofloxacin include rifampicin, intramuscular gentamicin and cotrimoxazole.⁵ Although the prognosis is on the whole good there may be residual loss of visual acuity, disc pallor, afferent pupillary defects and retinal pigmentary changes.