Visual Diagnosis: Sudden-Onset Decreased Vision in a Healthy Teenage Boy

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A 17-year-old healthy boy is admitted to the emergency department with sudden-onset decreased vision in his left eye. It is not associated with redness of the eye or ophthalmoparesis. In the previous 2 weeks, the patient has fully recovered from an upper respiratory tract infection with fever, myalgia, and cervical lymphadenopathy. He does not wear contact lenses, and there is no history of trauma.The adolescent has had no previous hospital admissions or surgeries. He has complete immunization according to the national vaccination program. He is institutionalized due to poor social support but spends weekends at his parents’ home in northern Portugal. The parents live in a rural zone, where he reports occasional contact with dogs and an unvaccinated young cat. There is no travel history outside of Portugal in the previous year.On physical examination he appears well. He has no fever, and his blood pressure is normal. There are no skin lesions and no cervical or axillary adenopathy. The neurologic examination findings are also normal. On ophthalmologic examination his visual acuity is 10 of 10 in the right eye and 3 of 10 in the left eye. His pupils are equal, round, and reactive to light, without a relative afferent pupillary defect, also known as Marcus Gunn pupil (an anomaly of pupils that respond differently to light shone in 1 eye at a time due to unilateral or asymmetrical disease of the retina or optic nerve). Dilated funduscopic examination of the left eye reveals sectoral disc edema inferiorly with suspected subretinal fluid in the nasal macula. Ocular coherence tomography reveals sectoral optic disc edema with intraretinal and subretinal fluid in the nasal macula extending under the fovea.Blood analysis reveals a mildly elevated C-reactive protein level of 17.6 mg/L (167.6 nmol/L), without leukocytosis or other abnormalities. Results of chest radiography are normal, and abdominal ultrasonography reveals mild splenomegaly without other anomalies. Brain and orbital magnetic resonance imaging results are normal.The patient is admitted to the hospital, and empirical antibiotic drug therapy is started with ciprofloxacin and azithromycin. A dilated funduscopic examination of the left eye reveals sectoral disc edema inferiorly, with formation of a discrete anterior macular star (Fig 1), which confirms the suspicion of neuroretinitis. Serologic studies identify the underlying diagnosis.Results of the polymerase chain reaction (PCR) assay for Bartonella, Borrelia burgdorferi, and Chlamydia trachomatis are negative. An immunologic study including an immunoglobulin count, antineutrophil cytoplasmic antibodies, and antinuclear antibodies is performed, and the results are normal. Results of serologic studies for human immunodeficiency viruses 1 and2, cytomegalovirus, Epstein-Barr virus, varicella-zoster, herpes simplex viruses 1 and 2, Treponema pallidum, toxoplasmosis, Borrelia burgdorferi, and rubeola are negative. Blood serologic tests for Bartonella henselae (performed by indirect fluorescence assay [IFA]) are negative for immunoglobulin (Ig) M and positive for IgG with a titer of 1:2048, establishing the diagnosis of acute neuroretinitis caused by B henselae.Neuroretinitis, a form of infectious optic neuropathy, is a rare disease characterized by acute vision loss due to optic nerve edema associated with stellate macular exudates, which are distributed in the peculiar form of a macular star. (1) In most patients, the disease is unilateral, as in our patient, but it can be bilateral in 5% to 30% of patients. (2)(3) It has a slightly higher incidence in the third and fourth decades of life and affects both sexes equally. (2)(3)The differential diagnosis of acute unilateral vision loss is broad, and ophthalmologic evaluation is required to distinguish the different entities because it may be caused by visual media problems (disorders of the cornea, anterior chamber, lens, and vitreous), retinal disease, or optic neuropathy (Table 1).In neuroretinitis, a form of infectious optic neuropathy characterized by optic disc swelling and hard macular exudates, patients usually present with painless acute unilateral visual loss, but, in some instances, there is eye pain or discomfort that may worsen with eye movements, making it more difficult to differentiate from optic neuritis. In this case, there may be associated fever, malaise, or headache, raising the suspicion for an infectious cause. Approximately 50% of patients have had a viral benign infection, usually affecting the respiratory tract, in the previous weeks. In the case of Bartonella infection, patients usually have a history of cat scratch, and lymphadenopathy is usually present. A small proportion of patients also develop arthritis, hepatitis, meningitis, or encephalitis, although these symptoms are rare.The visual acuity at initial evaluation is variable and can be completely normal. An afferent pupillary defect is usually present with optic disc edema. Partially depending on the timing of the ophthalmologic evaluation, optic disc edema can range from mild to severe. The macular exudates may be noticed only 2 weeks after the onset of symptoms, making it crucial to reevaluate patients who present with only acute papillitis, a form of optic neuropathy characterized by optic disc inflammation and deterioration, at first observation. The macular star persists for several weeks and then gradually diminishes, until its complete resolution in 6 to 12 months. (3)The pathogenesis and etiology of neuroretinitis are not yet completely understood. (3) The disease is caused by direct involvement of the optic nerve fibers, leading to edema and fluid exudation from the peripapillary retina. Infectious and immune diseases have been associated with the development of neuroretinitis. However, 25% to 50% of all cases remain idiopathic. (3)(4) The primary immune diseases associated with neuroretinitis are sarcoidosis, inflammatory bowel disease, polyarteritis nodosa, and IRVAN (idiopathic retinal vasculitis, aneurysms, and neuroretinitis) syndrome. (4) The main causes of infectious neuroretinitis are cat scratch disease and spirochetosis, namely, syphilis, borreliosis, and leptospirosis. Other causes include herpes simplex virus, hepatitis B, and paramyxovirus. As occurred in this patient, cat scratch disease is the most common infectious cause of neuroretinitis, occurring in approximately two-thirds of patients. (5)(6)Funduscopically, neuroretinitis is a great mimicker and may be confused with other conditions that cause unilateral optic disc swelling, such as papillitis and anterior ischemic optic neuropathy (characterized by ischemic insult of the optic nerve head with optic disc swelling, classified as arteritic or nonarteritic) (Table 2). (3) It is important to make a correct diagnosis, through a complete clinical history and prompt ophthalmologic evaluation, because neuroretinitis has a distinct pathogenesis and etiology.The definitive diagnosis of Bartonella infection is made by a positive serologic test result for Bartonella, a positive culture for Bartonella species, or PCR assay. The most used serologic test is IFA. IgG titers less than 1:64 indicate low probability of infection; IgG titers between 1:64 and 1:256 may represent possible infection, and the test should be repeated; IgG titers greater than 1:256 strongly suggest recent or active infection. A positive IgM, although representative of active infection, is rarely found because the production of IgM is usually brief. In the presence of a strong clinical suspicion of Bartonella infection, a negative serologic study should not exclude this infection because some recent studies have shown poor sensitivity and specificity for IFA serology. (7)(8) The identification of Bartonella in blood cultures is not frequent because it is a slow-growing gram-negative bacteria. The incubation period should be extended to at least 21 days, and, therefore, communicati

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