Orbital Myositis: Symptoms, Diagnosis, and Potential Treatments

Orbital myositis is a rare inflammatory condition affecting the extraocular muscles, leading to eye pain, swelling, and movement restrictions. While often idiopathic, it can be associated with autoimmune disorders or infections. Due to its variable presentation and overlap with other orbital diseases, timely recognition is essential for appropriate management.

Clinical Presentation

Patients typically experience abrupt periorbital pain, worsened by eye movement. This discomfort, often described as deep or pressure-like, distinguishes it from superficial ocular pain seen in conjunctivitis or dry eye syndrome. The pain is usually unilateral, though bilateral cases occur. Severity often correlates with inflammation, with some individuals reporting significant discomfort that disrupts daily activities.

Swelling of the eyelids and periorbital tissues is common, sometimes leading to mechanical ptosis if the upper eyelid is significantly involved. The inflammation may also cause conjunctival injection and chemosis, mimicking infectious or allergic conditions. Unlike bacterial orbital cellulitis, orbital myositis typically lacks systemic symptoms like fever or leukocytosis, though mild fatigue or malaise may be present.

Ocular motility disturbances are a hallmark, with patients reporting diplopia due to restricted movement of affected extraocular muscles. The limitation aligns with the inflamed muscle—medial rectus involvement impairs adduction, while superior rectus inflammation restricts upward gaze. This pattern helps differentiate it from cranial nerve palsies or myasthenia gravis. In severe cases, the affected eye may appear nearly immobile in certain directions.

Proptosis, or anterior displacement of the globe, may occur with significant muscle swelling. This is particularly evident when the inferior or superior rectus muscles are involved. Unlike thyroid eye disease, which often presents with bilateral and progressive proptosis, the protrusion in orbital myositis is usually acute and asymmetric. The degree varies, with some patients exhibiting subtle displacement and others experiencing noticeable bulging that can cause exposure-related symptoms like dryness or irritation.

Etiological Factors

Orbital myositis can arise spontaneously or be linked to systemic or infectious triggers. Idiopathic cases, where no clear cause is found, are common and diagnosed by excluding infectious, neoplastic, and autoimmune origins. Some researchers suggest an exaggerated inflammatory response to minor, unrecognized stimuli, such as viral antigens or environmental factors.

Infectious agents, particularly viruses like herpes simplex (HSV), varicella-zoster (VZV), and influenza, have been associated with post-viral inflammatory myositis, likely due to immune-mediated muscle damage. Bacterial infections, though less common, can contribute, especially in the setting of sinusitis. While fungal and parasitic infections are rare in immunocompetent individuals, opportunistic pathogens such as Aspergillus or Toxoplasma should be considered in immunosuppressed patients.

Autoimmune diseases frequently intersect with orbital myositis. Conditions such as granulomatosis with polyangiitis, systemic lupus erythematosus, and rheumatoid arthritis have been documented in association with the disease. In these cases, inflammation results from aberrant immune activation. Thyroid eye disease, though primarily involving fibroblast proliferation and fat expansion, can occasionally present with overlapping features, requiring careful differentiation.

Environmental and drug-related factors have also been explored. Some medications, particularly immune checkpoint inhibitors used in cancer therapy, may trigger orbital myositis as an adverse effect. These agents modulate immune responses and can inadvertently cause inflammation in non-target tissues. Additionally, allergic reactions and hypersensitivity responses have been postulated as rare but possible triggers, particularly in individuals with a history of atopy or systemic allergic conditions.

Diagnosis

Accurate diagnosis requires clinical evaluation and targeted diagnostic tests to differentiate it from other orbital inflammatory and infectious conditions. Imaging studies, laboratory tests, and, in select cases, biopsy procedures are essential.

Imaging Studies

Magnetic resonance imaging (MRI) with contrast is the preferred modality, as it provides detailed visualization of the extraocular muscles and surrounding soft tissues. Affected muscles typically exhibit diffuse enlargement with T2 hyperintensity and contrast enhancement, often sparing the tendinous insertions—a key distinction from thyroid eye disease. Computed tomography (CT) can be useful for rapid assessment, showing muscle swelling with associated fat stranding, though it lacks MRI’s soft-tissue contrast resolution. Imaging can also help identify adjacent sinus disease, orbital masses, or bony erosions that may suggest an alternative diagnosis.

Laboratory Tests

Bloodwork assesses systemic inflammation or associated autoimmune conditions. Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are common in active disease. Autoimmune panels, including antinuclear antibodies (ANA), rheumatoid factor (RF), and antineutrophil cytoplasmic antibodies (ANCA), may be warranted if an underlying disorder is suspected. Thyroid function tests, including thyroid-stimulating hormone (TSH) and thyroid-stimulating immunoglobulin (TSI), help differentiate orbital myositis from thyroid eye disease. Infectious workups, including viral serologies for HSV and VZV, may be considered in suspected post-viral cases.

Biopsy Procedures

Although rarely required, muscle biopsy may be indicated when the diagnosis remains uncertain or malignancy is a concern. Histopathologic examination typically reveals lymphocytic infiltration with muscle fiber degeneration and fibrosis, consistent with inflammatory myopathy. Immunohistochemical staining helps distinguish orbital myositis from neoplastic conditions, particularly in cases with atypical progression or poor response to therapy.

Classification Variants

Orbital myositis has distinct subtypes. Acute orbital myositis presents suddenly with pain, swelling, and restricted eye movement, often responding well to corticosteroids. Some cases exhibit a relapsing-remitting pattern, leading to progressive fibrosis and motility deficits.

Chronic orbital myositis develops gradually, with low-grade inflammation persisting for months. Unlike the acute form, it may present with minimal pain, with motility disturbances and orbital fullness being more prominent. This form often requires prolonged immunosuppressive therapy, as tapering corticosteroids can lead to recurrence.

Refractory orbital myositis, in which inflammation persists despite steroid therapy, may require second-line treatments such as biologic agents or cytotoxic immunosuppressants. In some cases, fibrosis leads to restrictive strabismus or fixed gaze limitations, necessitating surgical intervention.

Immune Pathways

The inflammatory process in orbital myositis involves both innate and adaptive immune responses. Cytokines such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interferon-gamma (IFN-γ) promote leukocyte infiltration, leading to tissue damage and edema.

T-cell involvement is a defining feature, with CD4+ helper T cells orchestrating the inflammatory cascade. Studies show increased expression of Th1 and Th17 cytokines, which sustain inflammation and may contribute to chronic disease. In some cases, B-cell activation leads to autoantibody production, further exacerbating inflammation. Regulatory T cells, which normally suppress excessive immune activation, appear dysfunctional in some individuals, allowing unchecked immune-mediated damage. These imbalances suggest potential for targeted immunotherapies to reduce inflammation while preserving immune function.

Possible Therapies

Treatment focuses on controlling inflammation and alleviating symptoms, with corticosteroids as the frontline therapy. High-dose oral prednisone, typically initiated at 1 mg/kg per day, often leads to rapid improvement. Tapering is done gradually to prevent relapse, though prolonged low-dose therapy may be necessary. Intravenous methylprednisolone is used in severe or refractory cases.

For patients who do not respond adequately to corticosteroids or experience frequent recurrences, steroid-sparing immunosuppressants such as methotrexate, azathioprine, or mycophenolate mofetil may be introduced. Biologic agents targeting specific cytokines, such as TNF-α inhibitors or IL-6 blockers, have shown promise in refractory cases. In cases where fibrosis leads to motility restrictions, surgical interventions such as extraocular muscle recession or orbital decompression may be considered. Ongoing research into novel immunomodulatory therapies continues to refine treatment strategies.

Systemic Associations

Orbital myositis frequently occurs alongside systemic conditions that influence its onset and progression. Autoimmune diseases such as systemic lupus erythematosus, Sjögren’s syndrome, and granulomatosis with polyangiitis have been reported in conjunction with extraocular muscle inflammation. In these cases, orbital myositis may serve as an early or isolated manifestation of systemic disease, necessitating comprehensive evaluation.

Beyond autoimmune conditions, orbital myositis has been observed in infectious and paraneoplastic contexts. Viral infections, particularly Epstein-Barr virus or cytomegalovirus, may trigger post-infectious immune activation leading to muscle inflammation. Paraneoplastic syndromes, though rare, should be considered in patients with atypical presentations or refractory disease, as malignancies such as thymoma or lymphoma can induce immune-mediated myositis. Recognizing these systemic associations is crucial for guiding treatment, as addressing the underlying condition significantly impacts disease control and prognosis.