40Chapter 2: Orbital disease or neurologic disease?

Table 2.1 Etiologies of orbital inflammatory disease

Sarcoidosis Syphilis Cysticercosis Lyme disease Whipple’s disease Herpes zoster

Inflammatory bowel disease Wegener’s granulomatosis Systemic lupus erythematosus Rheumatoid arthritis Scleroderma

Psoriatic arthropathy Giant cell myocarditis Kawasaki disease

response, about half of patients experience a later recurrence of orbital inflammation.

Diagnosis: Idiopathic orbital myositis

Tip: Orbital inflammation involving the superior rectus and levator muscles can mimic a superior division third nerve palsy. The presence of pain that is exacerbated by eye movement points to an orbital rather than intracranial process.

Painful optic neuropathy

Case: A 24-year-old waitress developed mild blurring of vision in the left eye associated with moderately severe periocular pain that was worse with eye movement. Three weeks after onset of symptoms, visual acuity was 20/20 in each eye and color vision was normal but there was a trace relative afferent pupillary defect (RAPD) on the left side. The right optic disc was normal, the left disc was mildly swollen. A brain MRI was normal. She received a presumptive diagnosis of idiopathic optic neuritis and was managed expectantly.

Her eye pain persisted and vision worsened further. On examination eight weeks after onset, her acuity had declined to 20/80 OS and she could identify only 5 of 15 color plates. There was now a

small but definite (1+) left RAPD. The left optic disc was still swollen and Goldmann perimetry demonstrated an inferior arcuate scotoma in the left eye (Figure 2.17). All findings in the right eye were normal.

Is this patient’s clinical course consistent with a diagnosis of optic neuritis?

The natural history of optic neuritis includes stabilization of vision and improvement of pain within two weeks of onset. Resolution of disc edema, if present, usually occurs by four weeks after onset. In contrast, this patient still had pain and disc edema eight weeks after onset, and her evaluation showed further progression of visual loss between the third week and eighth week. In addition, the pattern of visual loss (arcuate defect rather than central loss) would be unusual for demyelinating optic neuritis.

What specific feature of her clinical course raises the possibility of orbital disease?

Pain with eye movement that is severe and persistent is atypical for demyelinating optic neuritis and more suggestive of orbital inflammatory disease. An MRI of the orbits with contrast enhancement and fat suppression was obtained and showed enhancement around the left intraorbital optic nerve, indicating inflammation of the optic nerve sheath rather than the nerve itself (Figure 2.18). Blood tests for systemic inflammatory disorders were all normal or negative and a diagnosis of idiopathic optic perineuritis was made. She was treated with 80 mg of prednisone per day and experienced dramatic improvement of vision and complete resolution of pain. Her steroid dose was tapered over the next few months and she continued to do well.

Discussion: Inflammation involving the optic nerve sheath is termed optic perineuritis (OPN) and is considered a variant of idiopathic orbital inflammatory syndrome (described in the preceding case). Occasional cases of optic perineuritis are

due to a specific systemic inflammatory disorder such as sarcoidosis, Wegener’s granulomatosis, giant cell arteritis or syphilis (see Table 2.1 above), but in most cases inflammation is isolated to the orbit, and idiopathic. Although OPN shares some similarities with demyelinating optic neuritis, there are several clinical differences which are helpful for distinguishing between these two disorders (Table 2.2).

Similar to optic neuritis, idiopathic OPN affects women more often than men. The age range, however, is different: optic neuritis usually occurs in young adults whereas the age range in OPN is broader. Optic neuritis typically causes decreased visual acuity whereas in patients with OPN acuity is often spared. The natural history of these two disorders also differs. In contrast to the self-limited nature of optic neuritis, pain and visual loss in OPN

continue to progress. Unlike optic neuritis, patients with OPN show a dramatic response to steroids including a tendency to recur if steroids are discontinued too quickly.

The diagnosis of OPN is based on the radiographic (or occasionally histopathologic) findings. The characteristic picture is seen best on coronal post-contrast fat-suppressed MR images of the orbits, in which the inflammation of the optic nerve sheath appears as a bright doughnut of enhancement around the optic nerve. This radiographic

appearance resembles that of optic nerve sheath meningioma, but the presence of pain and acute visual loss in OPN contrasts with the insidious and usually painless presentation in patients with meningioma.

The importance of distinguishing OPN from optic neuritis concerns both treatment and prognosis. In terms of visual outcome, steroid treatment is considered optional for patients with optic neuritis whereas, without treatment, patients with OPN experience continued pain and progressive visual