Dovepress Vision, PML and multiple sclerosis signs in different functional systems. PML is primarily field testing should be performed every 3 months in patients known to occur in association with immunodef iciency treated with natalizumab for multiple sclerosis for longer than disorders, such as acquired immunodeficiency syndrome, one year. In close cooperation, neurologists and ophthalmolo- treatment with highly immunosuppressive agents such as gists could thus prevent an unnecessary delay in diagnosing rituximab, or rare congenital disorders like Wiskott-Aldrich natalizumab-associated PML and initiate early treatment of syndrome.2,3 However, PML is gaining importance in asso- this severe complication. Atypical clinical signs and unusual ciation with the increasing use and duration of natalizumab morphological findings on magnetic resonance imaging therapy in patients with multiple sclerosis. Natalizumab is should raise the suspicion of PML in a natalizumab-treated generally well tolerated and has sustained safety and efficacy patient with multiple sclerosis. in patients with active multiple sclerosis.4 On the other hand, the expected benefits of natalizumab have to be weighed against the risk of PML, and patients need to be selected and monitored carefully.5 With regard to multiple sclerosis, most of the ophthal- mological symptoms can be explained by optic nerve head disturbances. However, cortical involvement has to be taken into consideration in patients with nonspecific neurological signs and progression of the disease. The ophthalmologist plays a crucial role in being able to detect any deteriora- tion clinically without too much effort even at the bedside. Visual acuity and visual field examination are possible even in a very immunocompromised patient, and are completely noninvasive and cost-effective clinical measures. In this case, the main features leading to diagnosis of PML were detection of reactivated John Cunningham virus in the spinal fluid, in combination with deteriorating clinical symp- toms and findings on magnetic resonance imaging. There are data showing that natalizumab-associated PML and consecu- tive immune reconstitution inflammatory syndrome can be well managed in some cases.5 However, recent publications on this topic emphasize the critical importance of the time interval between diagnosis of PML, natalizumab cessation, and implementation of treatment for PML, resulting in a more favorable clinical course for this devastating disease.6 This case demonstrates that highly vigilant ophthalmo- logical observation of patients with multiple sclerosis on natalizumab can contribute to a fast diagnosis of natalizumab- associated PML.7–9 We suggest that visual acuity and visual Clinical Ophthalmology Publish your work in this journal Clinical Ophthalmology is an international, peer-reviewed journal covering all subspecialties within ophthalmology. Key topics include: Optometry; Visual science; Pharmacology and drug therapy in eye diseases; Basic Sciences; Primary and Secondary eye care; Patient Safety and Quality of Care Improvements. This journal is indexed on Submit your manuscript here: http://www.dovepress.com/clinical-ophthalmology-journal Clinical Ophthalmology 2012:6 Disclosure The authors report no conflicts of interest in this work. References 1. Metz I, Radue EW, Oterino A, et al. Pathology of immune reconstitu- tion inflammatory syndrome in multifocal sclerosis with natalizumab- associated progressive leukencephalopathy. Acta Neuropathol. 2012;123:235–245. 2. Downes S, Black GC, Hyman N, Simmonds M, Morris J, Barton C. Visual loss due to progressive multifocal leukoencephalopathy in a congenital immunodeficiency disorder. Arch Opthalmol. 2001;119: 1376–1378. 3. Clifford DB, De Luca A, Simpson DM, Arendt G, Giovannoni G, Nath A. Natalizumab-associated progressive multifocal leukoenceph- alopathy in patients with multiple sclerosis: lessons from 28 cases. Lancet Neurol. 2010;9:438–446. 4. Holmen C, Piehl F, Hillert J, et al. A Swedish national post-marketing surveillance study of natalizumab treatment in multiple sclerosis. Mult Scler. 2011;17:708–719. 5. Kappos L, Bates D, Edan G, et al. Natalizumab treatment for mul- tiple sclerosis: updated recommendations for patient selection and monitoring. Lancet Neurol. 2011;10:745–758. 6. Schröder A, Lee DH, Hellwig K, Lukas C, Linker RA, Gold R. Successful management of natalizumab-associated progressive multi- focal leukoencephalopathy and immune reconstitution syndrome in a patient with multiple sclerosis. Arch Neurol. 2010;67:1391–1394. 7. Vermersch P, Kappos L, Gold R, et al. Clinical outcomes of natalizumab-associated progressive multifocal leukoencephalopathy. Neurology. 2011;76:1697–1704. 8. Warnke C, Menge T, Hartung HP, et al. Natalizumab and progressive multifocal leukoencephalopathy: what are the causal factors and how can it be avoided? Arch Neurol. 2010;67:923–930. 9. O´Connor PW, Goodman A, Kappos L, et al. Disease activity return during natalizumab treatment interruption in patients with multiple sclerosis. Neurology. 2011;76:1858–1865. 10. Schaaf SM, Pitt D, Racke MK. What happens when natalizumab therapy is stopped? Expert Rev Neurother. 2011;11:1247–1250. Dovepress PubMed Central and CAS, and is the official journal of The Society of Clinical Ophthalmology (SCO). The manuscript management system is completely online and includes a very quick and fair peer-review system, which is all easy to use. Visit http://www.dovepress.com/ testimonials.php to read real quotes from published authors. submit your manuscript | www.dovepress.com Dovepress 1133