When orbital disease is mistaken for neurologic disease

In most patients with orbital disease, the clinical presentation includes signs and symptoms that help localize the disease process to the orbit. Typical features include eye pain or pressure, proptosis, periorbital swelling, eyelid abnormalities, conjunctival injection and chemosis. Difficulty recognizing that the disease localizes to the orbit may occur when these clinical manifestations are subtle or even absent. Mistakes in clinical localization may be further compounded by misinterpretation of radiographic studies, because imaging modalities designed to detect intracranial pathology are often inadequate for identifying orbital abnormalities.

In cases lacking obvious signs of orbital disease, there are usually other aspects of the history or examination that are helpful in localization; finding them may require a little additional effort and expertise. Eye pain in itself is non-localizing, but pain that increases with, or is provoked by, eye movement indicates an orbital rather than intracranial source. Diffuse conjunctival injection is readily appreciated but, when focal, may only be found by examining the globe in eccentric positions including manual elevation of the lid (Figures 2.1 and 2.2). Chemosis may be similarly focal.

Careful examination is also critical for detecting mild degrees of proptosis or enophthalmos. Changes in globe position are best detected by viewing the patient from above or below and observing globe position relative to the orbital rim (Figure 2.3). Making this judgement while seated directly in front of the patient is notoriously unreliable because our impression of globe position is always influenced

by lid position. Thus, lid retraction will be mistakenly perceived as proptosis (Figure 2.4C), whereas a smaller palpebral fissure (as in Horner syndrome) will be perceived as enophthalmos.

Certain eyelid abnormalities help to localize the disease process to the orbit. The lower lids demonstrate large variations in normal position. While most lower lids strike the globe at the lower limbus, many individuals exhibit a significant degree of inferior scleral show as a normal variation (Figure 2.4). Others have lower lids that rest a few millimeters above the limbus. Upper lid position is generally more consistent among normal individuals. The normal upper lid rests approximately 2 mm below the limbus. By definition, visible sclera above the superior limbus indicates a retracted lid. The presence of lid retraction is usually pathologic and is most commonly due to thyroid eye disease.

In this chapter we deal with cases in which a primary complaint of diplopia, visual loss or pain occurred in the relative absence of typical manifestations of orbital disease, and was therefore mistakenly attributed to intracranial disease. In each case, specific aspects of the history or examination should have raised concern for orbital disease, and these features are highlighted.

Incidental elevation deficit

Case: A 40-year-old interior decorator was referred for neurologic consultation because of recurrent headaches for several years. She was generally in good health and had no focal neurologic symptoms.

Figure 2.2 Young woman with orbital myositis. There is focal conjunctival injection over the left medial rectus insertion, best appreciated on eccentric gaze.

A

B

Figure 2.3 Examination technique for detecting proptosis.

(A) Patient with mild left proptosis. The appearance of the globes seems normal when viewed face-to-face. (B) When viewed from above it is evident that the left globe is in fact proptotic relative to the right, protruding beyond the brow ridge.

Physical examination was normal except for impairment of upgaze in the right eye. This was thought to represent a partial right third nerve palsy, and ancillary testing was therefore obtained. Brain MRI, CT of the orbits and a variety of blood tests were all normal or negative. A cerebral arteriogram was obtained to rule out an intracranial aneurysm, and results of this test were normal as well (see Chapter 10, Headache and third nerve palsy, for further discussion of imaging a suspected aneurysm).

She was referred for neuro-ophthalmic consultation. On examination, the eyes were aligned in primary position by cross-cover testing. Eye movements were full except for elevation of the right eye, which was limited, most prominently on gaze up and right (Figure 2.5). Saccadic velocity was normal in all directions, eyelid position and levator function were normal. Pupils were isocoric and briskly reactive to light.

What other mechanism could account for this patient’s abnormal ocular motility besides a third nerve palsy?

Limitation of elevation can occur from myopathy, orbital restrictive disease, neuromuscular junction disease or supranuclear disorders of gaze. In this case, preservation of normal alignment in primary position suggests a restrictive mechanism. A similar pattern may also be seen in supranuclear gaze palsies such as internuclear ophthalmoplegia and supranuclear monocular upgaze palsy, but in such cases there is prominent slowing of saccades. If the marked degree of limited elevation in this patient’s right eye were due to cranial nerve palsy, there would be a large angle right hypotropia in straight ahead gaze.

Review of her CT scan revealed an unrecognized blow-out fracture of the right orbital floor causing entrapment of the inferior rectus muscle (Figure 2.6). When these findings were reviewed with the patient, she recalled that at age eight she had fallen from a tree and struck her face, causing considerable bruising. At this point she realized that she had always had vague “blurring”

Figure 2.5 Ocular motility of a 40-year-old interior decorator with recurrent headaches. The eyes are normally aligned in primary position. Downgaze is full but elevation of the right eye is markedly limited, particularly in gaze up-right. (The pupils have been pharmacologically dilated.)

of vision on upgaze but had never sought medical attention for it. Difficulty recognizing that an ocular motility deficit is due to traumatic orbital disease may be particularly challenging in children in whom the traumatic event was unwitnessed. Ocular motility deficits may be present in the absence of external signs of trauma, sometimes termed a “white-eyed blowout”. In this syndrome, a trapdoor orbital floor fracture incarcerates the inferior rectus, producing limitation of upgaze, as in the above patient.

Based on the above findings, this patient’s motility disturbance was diagnosed as a long-standing muscle entrapment. As she was essentially asymptomatic, no specific treatment was indicated. Her headache pattern was consistent with migraine and was managed accordingly.

Discussion: The limited elevation of the right eye in this patient, particularly in gaze up and to the right, suggested weakness of the right superior rectus muscle, and extensive investigation was therefore undertaken for a presumed partial third nerve palsy. But her ocular motor problem was actually due to restriction of the inferior rectus muscle. Orbital restrictive disease, also termed restrictive orbitopathy, is characterized by loss of normal elasticity of an eye muscle, causing limited eye movement in a direction opposite to the action of the involved muscle (Figure 2.7). In this case, the inferior rectus muscle was entrapped in a longstanding but undiagnosed orbital floor fracture which caused tethering of the globe on attempted upgaze. In some cases of post-traumatic restrictive disease the muscle is not actually entrapped in the fracture but has lost elasticity due to scar-

ring. Graves’ disease (thyroid eye disease) is another common cause of restrictive orbitopathy, often producing the same pattern seen here. Other less common forms include idiopathic orbital inflammation (orbital myositis), orbital tumors and iatrogenic events (e.g. inadvertent orbital penetration during sinus surgery).

Restrictive orbitopathy may involve one, several or all the extraocular muscles, and thus the pattern and magnitude of ophthalmoplegia depend on the muscles affected. Restrictive orbitopathy often mimics a neurologic ocular motor disorder; for example, a restricted medial rectus muscle produces an abduction deficit that simulates a sixth nerve palsy (Figure 2.8). In such cases, it is usually possible to distinguish between cranial neuropathy and orbital restrictive disease on clinical grounds without depending on neuro-imaging to identify the pathology.

Preserved alignment in primary position is not an invariable feature of restrictive orbitopathy but when present it is a very helpful finding. Normal saccadic velocity is another clue favoring restrictive orbital disease. Limitation of eye movement due to cranial nerve palsy or supranuclear disorders is

A

B

Figure 2.8 Restrictive orbitopathy due to thyroid eye disease. (A) There is incomplete abduction of the left eye, suggesting a left sixth nerve palsy and a right hypotropia. Bilateral lid retraction and conjunctival injection suggest the correct diagnosis of Graves’ disease. (B) Axial non-contrast orbital CT shows fusiform enlargement of the medial rectus muscles, left greater than right.

typically accompanied by slowing of saccadic velocity. In contrast, the two conditions in which normal saccadic velocity is preserved despite eye movement limitation are restrictive orbitopathy and myasthenia. This differential feature is less helpful in cases with only minimal limitation of eye movement, in which slowing of saccadic velocity may be difficult to detect without the aid of recording devices.

The fact that only one eye muscle was involved in the above case was an additional helpful feature. If this patient’s ocular motor dysfunction were due to a third nerve palsy, it would be a partial one. While partial third nerve palsies are common, isolated weakness of just one extraocular muscle is an extremely unusual presentation. Thus, it is important to consider other diagnostic possibilities when only one eye muscle is paretic, including myasthenia, internuclear ophthalmoplegia, myopathy and orbital restrictive disease.

Diagnosis: Orbital floor fracture with muscle entrapment

Tip: Restrictive orbitopathy can mimic neurologic ocular motor disorders. Normal ocular alignment