Linear sebaceous nevus syndrome (LSNS) was first described by Feuerstein and Mims in 1962.1 It is a rare disorder comprising the triad of sebaceous nevus, seizures, and mental retardation in varying degrees of phenotypic expression. The sebaceous nevus, which is essential for diagnosis, may be of any size and is often linear and localized on the head or neck. Up to 50% of patients with LSNS have ocular involvement.2–4 These include limbal choristomas, ptosis, strabismus, colobomas of the eyelid, iris, and retina, and staphylomas.1 The extracutaneous manifestations involve the brain, eye, cardiovascular, urogenital, and skeletal systems.4 The association of LSNS and rod-cone dystrophy has not been reported. To our knowledge, this is the first case of a patient with LSNS with rod-cone dystrophy.
The patient was born in Canada in 1988 to a 35-year-old gravida 2 para 1 mother via an uncomplicated normal vaginal birth. At birth, a large nevus covering the right side of his face and scalp was noted. There was bilateral asymmetric ptosis, greater on the right. Ocular examination revealed a large, superotemporal limbal dermoid in the right eye extending into the visual axis (Figure 1A). A similar but smaller lesion was noted in the left eye, extending 1 mm into the cornea (Figure 1B). Corneal clouding was noted as greater on the right than the left. Dilated funduscopic examination revealed bilateral posterior staphylomas. Visual acuity and cycloplegic refraction from this time were not available. A diagnosis of linear sebaceous nevus syndrome was made.
(A) Right and (B) left anterior segment at age 20 years.
Follow-up at age 4 years revealed significant anisometropia with a refraction of +250 −300 × 145 in the right eye and −800 −200 × 160 in the left eye. Best-corrected visual acuity was 6/24 in the right eye and 6/12 in the left eye. Left peripheral retinal degeneration was noted and reportedly treated with cryopexy. His amblyopia was treated with patching. At this time, he underwent six plastic surgical procedures to remove the large congenital nevus on the right side of the face. Histopathologic examination showed no signs of malignancy.
From age 5 years, the patient was reviewed regularly at the Sydney Eye Hospital, Australia. Between the ages of 5 and 11 years, his visual acuity and overall condition was relatively stable. At age 12 years, the patient complained of increasing difficulty with vision at school, mild photophobia, and nyctalopia. Funduscopic examination demonstrated irregular retinal changes and significant posterior staphylomas and small and tilted discs characteristic of high myopia. Arteriolar attenuation was present. However, no cystoid macular edema, posterior subcapsular cataract, pigmented cells in the vitreous, reticular changes, or salt and pepper fundus changes characteristic of retinitis pigmentosa were noted.
Full-field electroretinography (ERG) was performed in May 2001. Normal amplitudes for both photopic and scotopic testing conditions were demonstrated, but there was delayed latency under scotopic conditions, indicating early rod system dysfunction.
Over a 12-month period, the patient complained of a decrease in peripheral vision that was confirmed with Goldmann perimetry. Serial ERG over the following 7 years confirmed and demonstrated a progression of rod-cone dysfunction that was asymmetrical (the right worse than the left) (Figure 2). Electrooculographic testing was consistently normal.
Selected graphs of electroretinography performed April 2008 demonstrating decreased amplitude of a-waves (dark max 3 [right eye only], single flash cone) and b-waves (dim white, single flash cone, 30-Hz flicker) with delayed latency demonstrated in a-waves (single flash cone) and b-waves (30-Hz flicker) in both the right and left eye that indicate rod-cone dysfunction. Note that the right eye is more affected than the left; the exception being under single flash cone testing conditions, where the left eye shows a greater attenuation of a-wave amplitude compared with the right. The greater attenuation of a-waves in the left eye under these conditions is in fact a reflection of the high myopia in the left eye because the latency is near normal. In contrast, the right eye has decreased latency and attenuated a-waves under single flash conditions and reflects retinal dysfunction.
ERG remains the best available test to objectively assess retinal function.5 The diagnosis of rod-cone dystrophy was confirmed in our patient with the abnormal ERG and normal electrooculograph findings. The full-field ERG in our patient showed a marked reduction of both rod and cone signals, characterized by reduced a- and b-waves, as well as delayed latency.
In early rod-cone dystrophy, ERG may show normal a-wave amplitude but abnormally delayed a-wave latency.6 With disease progression, both amplitude and latency are affected, indicating widespread photoreceptor abnormality.6 In this patient, serial ERG showed characteristic deterioration in both amplitude and latency of photoreceptor signals under both photopic and scotopic conditions seen in rod-cone dysfunction, with the right worse than the left.
Importantly, these changes are distinct from the ERG changes found in patients with high myopia. A recent study found myopic patients have attenuated a- and b-wave amplitudes but normal latency.6–8 This can been seen under single flash cone ERG testing conditions in our patient’s left eye, where there was greater attenuation of the a-wave compared with the right eye, but the left eye had near normal latency and the right eye had delay latency combined with attenuated a- and b-wave latencies. Although the ERG changes may be relatively subtle, they are more pronounced with increasing axial length.6,8
The clinician should be aware of the importance of excluding associated retinal pathology in patients with high refractive error. This is relevant because myopia is a common association in retinal dystrophies such as congenital stationary night blindness, x-linked retinitis pigmentosa, cone dystrophies, and some rod-cone dystrophies.6 Electrophysiological testing is particularly relevant if patients have suggestive symptoms including nyctalopia, even with a normal fundus appearance.9 We suggest that there be a low threshold for performing electrophysiological testing in such patients.
It should also be noted that, to the best of our knowledge, peripheral retinal degeneration and its treatment, such as outpatient cryopexy, does not have any known associations with LSNS or rod-cone dystrophy.
Because LSNS is a multisystem disorder, it is important that treatment of such patients involves an interdisciplinary approach. This case illustrates that rod-cone dystrophy may be associated with LSNS. Unless clinical suspicion is high, this association may be missed despite suggestive symptoms.
- Feuerstein RC, Mims LC. Linear nevus sebaceous with convulsions and mental retardation. Am J Dis Child. 1962;104:675–679.
- Insler MS, Davlin L. Ocular findings in linear sebaceous nevus syndrome. Br J Ophthalmol. 1987:71:268–272 doi:10.1136/bjo.71.4.268 [CrossRef]
- Duncan JL, Golabi M, Frederick DR, et al. Complex limbal choristomas in linear nevus sebaceous syndrome. Ophthalmology. 1998;105:1459–1465. doi:10.1016/S0161-6420(98)98029-0 [CrossRef]
- Menascu S, Donner EJ. Linear nevus sebaceous syndrome: Case reports and review of the literature. Pediatr Neurol. 2008;38:207–210. doi:10.1016/j.pediatrneurol.2007.10.012 [CrossRef]
- Marmor MF, Holder GE, Seelinger MW, Yamamoto S. International Society for Clinical Electrophysiology of Vision Standard for clinical electroretinography. Doc Ophthalmol. 2004;108:107–114. doi:10.1023/B:DOOP.0000036793.44912.45 [CrossRef]
- Flitcroft DI, Adams GGW, Robson AG, Holder GE. Retinal dysfunction and refractive errors: an electrophysiological study of children. Br J Ophthalmol. 2005;89:484–488. doi:10.1136/bjo.2004.045328 [CrossRef]
- Malik SRK, Gupta AK, Gupta PC, Singh G. ERG in myopia. Indian J Ophthalmol. 1969;17:48–51.
- Westall CA, Panton CM, Dhaliwal HS, Sigesmund DA, Levin AV. The electroretinogram in high myopia. Doc Ophthalmol. 2001;102:115–130. doi:10.1023/A:1017535207481 [CrossRef]
- Chia A, Luu CD. Electrophysiological findings in persons with nyctalopia. Ann Acad Med Singapore. 2006;35:864–867.