Idiopathic orbital myositis in a pregnant woman

Summary

Orbital myositis (OM) is the second most common cause of extraocular muscle disease with thyroid-related orbitopathy being by far the most common.

OM may be idiopathic or secondary to inflammatory, infective, neoplastic or drug causes. Idiopathic orbital myositis (iOM) may be distinguished by its characteristic presentation and imaging findings, absence of thyroid dysfunction and autoimmunity and rapid response to corticosteroid therapy.

Case report

A 29-year-old woman in the 25th week of her first pregnancy presented to the emergency department with a 24 h history of painful diplopia associated with periorbital oedema. The patient denied recent trauma or infective symptoms. Her pregnancy had been previously uneventful, and she did not report any significant previous medical history.

Examination revealed periorbital oedema giving an “S-shaped” appearance to the eyelid (Figure 1). Best-corrected Snellen visual acuity was 6/7.5 bilaterally. There was a mild abduction and adduction deficit of the left eye with mild diplopia on adduction. Fatigue was not present on conjugated upward gaze. Pupils were equal and reactive to light with no relative afferent pupillary defect. Optic nerve function and colour vision was found to be normal. Slit lamp assessment was normal apart from mild injection at the left lateral rectus muscle insertion. Intra-ocular pressures and dilated fundus examination were normal. The woman was afebrile, she appeared clinically euthyroid and there was no evidence of lid lag or lid retraction. No abnormalities were detected on skin or joint examination. The cardio-respiratory examination was unremarkable as was the remainder of the neurological examination.

OPEN IN VIEWER

Figure 1.

Left-sided “S-shaped” periorbital swelling and inward torsion of the left eye.

The full blood count revealed a white cell count of 11.3 × 109/L (normal range 6.2–14.8 × 10⁹/L) with neutrophils 8.49 × 10⁹/L (normal range 3.8–12.3 × 10⁹/L). Thyroid function was normal and thyroid stimulating hormone receptor antibodies (TSHRAb) were negative. Immunoglobulin-G 4 (IgG4) and serum angiotensin converting enzyme levels were normal. C-reactive protein (CRP) was 13 mg/L (normal <6 mg/L) and anti-nuclear and anti-neutrophil cytoplasmic antibodies were negative. Magnetic resonance imaging (MRI) without gadolinium demonstrated an expanded left lateral rectus muscle belly and heterogeneously increased T2 signal with a cuff of surrounding oedema in the left retro-orbital fat, consistent with OM (Figure 2). Prednisolone 25 mg daily was commenced. One week later, inflammation at the lateral rectus muscle insertion had resolved clinically and there was no longer any ocular motility deficit. Repeat MRI 3 weeks after presentation demonstrated resolution of myositis (Figure 3). Prednisolone was weaned and ceased after 4 weeks of treatment without recurrence of myositis. The patient delivered a healthy female with a birth weight of 3.57 kg at 40 weeks’ gestation.

OPEN IN VIEWER

Figure 2.

T2 axial (A) and coronal (B) magnetic resonance imaging image demonstrating an expanded left lateral rectus muscle belly (arrows) with heterogeneously increased T2 signal with a cuff of surrounding oedema in the left retro-orbital fat laterally involving both intra- and extraconal space.

OPEN IN VIEWER

Figure 3.

T2 axial (A) and coronal (B) magnetic resonance imaging images 3 weeks after initiating corticosteroid treatment demonstrating resolution of myositis.

Discussion

OM is a rare condition, which typically presents with acute or subacute onset of gaze-evoked orbital pain, diplopia, eyelid swelling, mild ptosis and limitation of eye movements, typically resolving within days to weeks of corticosteroid therapy. ¹ Rarely, OM may be associated with painful diplopia without clinical evidence of orbital inflammation. ² iOM is the most common form, and typically affects young females. A single extraocular muscle (EOM) is involved in 68% of cases, two muscles in 22% and three or more in 10%. Bilateral involvement with iOM is rare (1.3% of cases).

Typical MRI findings with OM include thickening of the affected EOM and tendinous insertion with uptake of gadolinium, signal-intensity hyperintensity on T2-weighted images and localised inflammation on fat-suppressed T2-weighted images. ³

OM may also occur with systemic disease including IgG4-related ophthalmic disease (IgG4-ROD), inflammatory bowel disease, sarcoidosis, connective tissue disease, post-infective, medications (immune checkpoint inhibitors, bisphosphonates, statins) and as a paraneoplastic phenomenon. OM with underlying causes is more commonly bilateral with involvement of multiple EOMs. ¹ Secondary causes should be sought when assessing a pregnant woman with OM. IgG4-ROD is the most common condition associated with OM. Involvement is bilateral in 51.4% of cases and multiple muscles are usually involved. Patients with IgG4-ROD rarely have pain with eye movements and ocular movements are relatively normal. ¹ Diagnostic criteria for IgG4-related disease are based on organ enlargement/dysfunction or nodular lesions/masses, increased serum IgG4 concentration (over 1.35 g/L), and infiltration of IgG4+ cells (more than 10 cells/high power field and IgG4 + /IgG+ cell ratio over 40%). ⁴ Therefore, imaging, serology and histopathological studies are required when assessing for IgG4-ROD. Inflammatory bowel disease (IBD) can also precipitate OM. OM associated with IBD is bilateral in 45.2% of cases and multiple EOMs were involved in 67.8%. ¹ Symptoms of OM may precede the onset of IBD symptoms. ¹ Endoscopic evaluation is required in any case where IBD is suggested on history or physical examination. Immunosuppressives, in addition to corticosteroid therapy, were required in 43% of patients with OM associated with IBD. ¹ OM with orbital sarcoidosis is usually bilateral with involvement of multiple EOMs. ¹ Diplopia is usually painless and swelling may be absent. Sarcoidosis of other sites is commonly found on imaging. The diagnosis of ocular sarcoidosis relies upon a compatible clinical and radiologic presentation, pathologic evidence of non-caseating granulomas, and exclusion of other diseases with similar findings, such as infections or malignancy. ⁵ As with iOM, sarcoidosis-associated OM responds well to corticosteroids. ¹ When OM is associated with systemic lupus erythematosus (SLE) it is usually bilateral and acute in onset. ¹ A positive antinuclear (ANA) and anti-neutrophil cytoplasmic antibodies (ANCA) along with characteristic clinical features, haematological and biochemical findings would support a diagnosis of SLE as an underlying cause of OM.

In addition to secondary causes of OM, there are a number of differential diagnoses that should be considered when a pregnant woman presents with diplopia, painful eye movements, erythema and swelling.

Thyroid-associated orbitopathy (TRO) is the most common cause of extraocular muscle dysfunction. TRO is typically bilateral though may be asymmetric, associated with proptosis, tearing and orbital oedema, and in severe cases, conjunctival inflammation. The lateral rectus is usually less severely affected. Lid lag and retraction may occur with hyperthyroidism. TRO may be differentiated from OM by the presence of TSHRAb antibodies, and hyperthyroidism, which is present in 90% of patients. Radiologically, swelling of orbital fat and absence of thickening of tendinous insertions of EOM result in a “coke bottle” appearance.

Myasthenia gravis is associated with variable degrees of diplopia, unilateral or bilateral ptosis and fatiguability. Eye pain is usually absent. Impaired ocular movements typically do not conform to involvement of one ocular muscle or nerve. Acetylcholine receptor antibodies are highly specific; however, sensitivity may be as low as 50% in ocular myasthenia.

Wernicke syndrome secondary to thiamine deficiency may result in vertical or horizontal diplopia; however, ptosis and eye pain are usually absent, and gait ataxia and encephalopathy may be present.

Wernicke encephalopathy should particularly be considered in pregnant women with severe hyperemesis gravidarum or previous history of bariatric surgery.

Posterior scleritis presents with moderate-to-severe boring eye pain worse nocturnally, exacerbated by extraocular motility or touch, and associated with ocular redness, photophobia and tearing. It may also be associated with vision loss due to optic nerve or retinal compression. Orbital imaging usually demonstrates choroidal thickness.

Orbital cellulitis may present similarly to OM; however, fever is usually a predominant feature, ocular pain may be independent of movement, and ophthalmoplegia with diplopia, chemosis and decreased or blurred vision may be present. Neutrophil leucocytosis and elevated inflammatory markers are commonly present; typical organisms include staphylococci and streptococci; aspergillus and mucormycosis may affect immunocompromised individuals.

Orbital tumours are usually differentiated from orbital myositis radiologically rather than clinically. The Tolosa–Hunt Syndrome is a rare inflammatory condition, which is also associated with painful ophthalmoplegia. It is commonly associated with ipsilateral motor nerve palsies, oculosympathetic paralysis and/or sensory loss of the 5th cranial nerve. Other differential diagnoses, which would lead to diplopia without gaze-evoked orbital pain or eyelid swelling and erythema, include internuclear ophthalmoplegia and EOM entrapment secondary to trauma.^6,7

Diagnosis of iOM is based on the characteristic presentation and MRI findings, absence of clinical and biochemical thyroid dysfunction and thyroid antibodies, exclusion of underlying causes, and response within 1 month of commencing corticosteroid therapy.

A total of 24 cases of iOM related to pregnancy have been reported.^7–9 Information on the timing of presentation was available in 12 cases; OM occurred de novo during the third trimester in six cases, recurred following preconception disease during pregnancy in three cases, and initially presented postpartum in three women. The lateral rectus was the most commonly affected EOM.

Mild disease was successfully treated with non-steroidal anti-inflammatories or short-term systemic corticosteroids. Most cases did not recur on cessation of treatment. However, in those that did have a further episode, they recurred multiple times both during pregnancy, peri-partum and in subsequent pregnancies. ⁹

Conclusion

We present a case of iOM during the second trimester of pregnancy, which resolved promptly with oral corticosteroid treatment, without recurrence. Obstetric physicians should be aware of the differential diagnoses of the pregnant woman who presents with painful diplopia, restriction of extraocular movements and periorbital oedema.