Cat-Scratch Disease

Prepared for the American Uveitis Society by Alexander C Tsang, MD April 2003

University of Texas Medical Branch, Galveston, TX

Introduction

Cat-scratch disease (CSD) is caused by a bacterium, Bartonella henselae. The most common manifestations of CSD are skin lesions and lymph node enlargement. The eye is involved in a minority of cases (less than 10%) of CSD. Usually only one eye is affected. The most commonly reported manifestations in the eye are conjunctivitis ("pink eye"), lesions on the eyelid (bacillary angiomatosis), and optic nerve swelling with a "macular star" (neuroretinitis), a characteristic pattern of yellow fatty material which collects in the center of the retina. Other forms of CSD associated ocular inflammation occur less commonly. CSD is slightly more prevalent in Southern states and in younger people.

History

The connection between Bartonella bacteria and CSD was not realized until the 1980s. Prior to this, the observation that affected patients were usually in close contact with cats lent the disease its name. In 1983, investigators identified the Rochalimea species of bacteria as the causative agent. Two species in this family, Rochalimea henselae and Rochalimea quintana, are closely related. These organisms were reclassified into the Bartonella family of bacteria in the early 1990's. Patients with B. henselae infections may have false positive tests for B. quintana.

Course of Disease

Although cat exposure was associated correctly with CSD prior to the discovery of Bartonella, it is now realized that CSD can occur without cat scratches or even cat exposure; in fact, Bartonella has been identified in cattle, coyotes, dogs, and other animals. Up to 50% of domestic cats carry B. henselae, with kittens less than one year of age the most common carriers. Fleas transmit the disease between cats and other hosts and may be an intermediate vector for human disease. The incubation time from bacteria exposure to symptoms ranges from one to several weeks.

Initial symptoms of CSD resemble those of a flu-like illness (general weakness, low-grade fever, headache, spleen enlargement, joint or muscle pain) and may not be noticed or recalled by patients. Enlarged regional lymph nodes in the armpit, groin, upper neck, or head frequently follow.

Parinaud's oculoglandular syndrome (POGS) is an unusual type of conjunctivitis, or "pink eye". In POGS, the conjunctivitis is sometimes described as granulomatous, which indicates the large, red, vascular bumps present on the inside of the eyelids and sometimes the eyelid skin. A lymph node in front of the ear on the same side of the face as the conjunctivitis is frequently swollen. POGS occurs in 6% of cases of CSD, making it the most common ocular manifestation of this disease.

Bacillary angiomatosis (BA) describes a red lesion which may appear on the eyelid or conjunctiva. It is uncommon and requires a biopsy for definitive diagnosis. Bartonella has also been reported to cause vascular lesions on the surface of the optic nerve, a condition sometimes referred to as peripapillary angiomatosis.

Patients who develop the ocular complication of neuroretinitis (swelling of the optic nerve and retina) may notice blurring or alteration of vision, sometimes with an enlarged blind spot. Swollen lymph nodes, pain, and external signs of CSD are usually not present. Examination shows swelling of the optic nerve head with a "macular star". (Figure 1) The term "macular star" stems from the pattern of bright streaks in the center of the retina. These streaks are made of lipid, a fatty substance normally found in the blood. The lipid is left behind after the fluid causing swelling of the macula gradually goes away, much as salt is left behind on the ground when salt water evaporates. This condition is usually in one eye only. Recovery occurs with or without treatment and because of this, the need for treatment is controversial. Recovery may take several months.

Inflammation of other portions of the eye, including the iris and ciliary body in the front of the eye, the vitreous (gel in the back of the eye) , retinal blood vessels, and the sclera (white of the eye) may occur with CSD. In such cases, the patient may notice eyeball tenderness, light sensitivity, and blurred vision. Identification of the specific inflamed structures requires a complete examination by an ophthalmologist, sometimes requiring extra diagnostic tests such as fluorescein angiography..

Figure 1 Left hand image: Optic nerve swelling with macular star (arrows). Right hand image: Dye test of same eye showing inflammation of optic nerve head (arrow)

(Photographs courtesy of Dr. Suketu Patel)

Diagnosis and Testing

The diagnosis of CSD has been revolutionized by the ability to test the blood for antibodies (blood proteins that react against infections) against B. henselae, providing evidence of infection. This replaces the old lab methods of diagnosis which relied on surgical biopsy of an involved lymph node. A new technique, the polymerase chain reaction (PCR) is also gaining popularity as a species identifying diagnostic tool. PCR testing confirms presence of bacterial remnants in a submitted sample, and has great promise for the future.

Treatment

Many antibiotics have been shown to kill or stop the growth of Bartonella. For skin, lymph node and ocular lesions, oral ciprofloxacin, rifampin, doxycycline, sulfamethoxazole/trimethoprim (Bactrim or Septra), and/or gentamicin injections may be effective. In less severe cases, erythromycin or azithromycin may be used.. As noted above, some clinicians do not treat neuroretinitis with antibiotics since most patients have an excellent visual recovery even without their use. Corticosteroid or other anti-inflammatory drugs may be prescribed along with antibiotics, however there is no conclusive evidence that corticosteroid therapy is beneficial in speeding or improving recovery.

Cause of Condition

As detailed above, the bacterium Bartonella henselae has been identified as the cause of CSD.

Prognosis

Cat-scratch disease in the eye generally has a very good visual outcome, although patients with neuroretinitis may be left with residual symptoms including an enlarged blind spot, visual field defect(s), and altered color sensitivity. Vision returns to 20/40 or better in over 90% of patients in most reported case series of patients with neuroretinitis.

Research and Future Outlook

Further information is needed to determine the ideal treatment regimen for patients with CSD, including identification of whether antibotics and corticosteroids are of benefit.