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A 40 year old woman with decreased vision for one year
Digital Journal of Ophthalmology 2003
Volume 9, Number 2
June 23, 2003
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| Diagnosis and Discussion | Diagnosis: Pseudoxanthoma elasticum with optic neuropathy following intracranial aneurysm surgery
Pseudoxanthoma elasticum (PXE) is a disorder of elastic connective tissue that affects multiple organ systems: namely, the eyes, skin, GI tract and cardiovascular system. It is rare, with an incidence of 1 per 160,000 and is more commonly found in females. The inheritance, most commonly autosomal recessive, can also be sporadic or dominant with variable penetrance.
The pathophysiology of PXE involves progressive calcification of elastin fibers throughout the body, resulting in elastic tissues in various vessels and organs becoming more brittle. Studies have shown that PXE patients have an abnormal gene on Chromosome 16 that codes for a transmembrane transporter protein (1). One theory is that this defect results in abnormal calcium accumulation in the extracellular elastic matrix. Another theory is that this transporter causes production of abnormal glycosaminoglycans in the extracellular matrix, which somehow promotes excessive calcium deposition. The true biomolecular pathophysiology is still largely unknown.
On ophthalmic exam, approximately 85% of patients with PXE have angioid streaks in the retina. Conversely, approximately one third of patients with angioid streaks have pseudoxanthoma elasticum. Other systemic diseases that should be considered in a patient with angioid streaks include Paget's disease of bone, sickle cell disease/trait, other hemoglobinopathies, and Ehlers-Danlos syndrome.
Angioid streaks appear as breaks or dehiscences in Bruch's membrane with overlying pigment epithelial atrophy and disruption of the underlying choriocapillaris. These are usually bilateral and found posterior to the equator. It is thought that the extrinsic forces of the extraocular muscles on a calcified, brittle Bruch's membrane are a possible cause of these breaks, which are acquired and progressively worsen with age. Early hyperfluorescence of the streaks on fluorescein angiogram is secondary to the overlying pigment epithelial atrophy. Persistent staining of the streaks late in the fluorescein angiogram is another characteristic finding.
Frequent ophthalmic examinations are mandated in patients with angioid streaks because of their tendency to develop choroidal neovascular membranes (CNVM). CNVM in patients with PXE frequently are vision threatening, and a majority of these individuals become legally blind by age 50. Features of angioid streaks that predict a poor prognosis are length, distance from the fovea, and whether they are diffuse, or appear like a cracked egg shell(2). Because even minor ocular trauma can cause subretinal hemorrhages, patients should be encouraged to use eye protection and avoid contact sports. Laser photocoagulation has been used to treat CNVM in these patients, with limited success(3). There is a case reported of a successful treatment of CNVM in a patient with PXE with submacular translocation(4).
Other ophthalmic findings in PXE include a peau d'orange fundus appearance, which due to RPE degeneration presumably secondary to alterations in Bruch's membrane. Salmon spots can also be seen and appear as small, round yellow lesions also due to RPE atrophy and degeneration of Bruch's membrane. Patients with PXE have also been reported to have a higher incidence of macular and optic nerve drusen.
Patients with PXE tend to have systemic disorders related to calcification of elastin in blood vessels and skin. Skin findings in these patients include a plucked chicken appearance consisting of waxy, yellow papules commonly seen on the neck, axillae, and periumbilical regions. Elastin calcification in blood vessels leads to hypertension, intracranial aneurysms, cerebral ischemia, coronary artery disease, and gastrointestinal bleeds. Intracranial aneurysms in these patients are potentially life threatening and should always be considered in patients with PXE and neurological symptoms. Ischemic optic neuropathy can occur in these patients as a result of gastrointestinal bleeds(5) or status-post intracranial aneurysm surgery from ischemia or direct surgical manipulation(6).
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