Idiopathic orbital inflammatory syndrome (IOIS), also known as orbital pseudotumor, is a non-infectious inflammation of the orbital soft tissues for which no cause is found after local and systemic evaluation.¹ It can be diffuse or localised.² The localized type of idiopathic orbital inflammation is further subdivided into myositis, periscleritis, perineuritis and dacryoadenitis.3 We present a case of orbital myositis with unique presentation.

A 30 years female patient presented in OPD  with chief complaints of diplopia for two days  and drooping of right eyelid for one day. Diplopia was binocular and when looking towards right side and upwards. Patient also complained of ocular pain and  headache for preceeding ten days. The headache was  acute in onset, severe in intensity and intermittent in nature and was referred  to right eye. For this pain, patient  took some oral analgesic from local practitioner.There was no history of fever, sorethroat ,neck rigidity, ocular  trauma, any preceding infection or any other systemic illness. There was no significant  past history, treatment history and family history.

General physical examination was normal. On ocular examination ,complete ptosis was present in right eye (Figure 1a). Visual acuity was 6/12 (with PH 6/6) in right eye and 6/6 in left eye on Snellen,s visual acuity chart. It was obtained in right eye by lifting upper eyelid manually. Bilateral Pupils were normal in size and reacting normally  to light. Intraocular pressure and colour  vision was normal in both eyes. In extraocular movements abduction and elevation was restricted in right eye ( Figure 1b & 1c), adduction and depression was normal in right eye (Figure 1d &1e) and  the extraocular movements were full in left eye in all gazes. Diplopia was present in dextroversion and elevation, but more in  elevation. There was no lid oedema, chemosis or any localised conjuctival congestion. On Slit lamp examination, anterior and posterior segment revealed no abnormality. There was no audible bruit on auscultation over the right eye. The remainder of the neurological examination was normal.

A differential diagnosis of thyroid ophthalmopathy, Tolosa Hunt syndrome, ocular myasthenia, orbital neoplasm and lymphoproliferative infiltration was considered. Laboratory investigations and radiological investigations were done. Complete hemogram, blood sugar level, liver function test, renal function tests and thyroid function tests were normal. Rheumatoid factor and antinuclear antibody  were negative. Ice pack test was  negative.

MRI Orbit (Plain&contrast) showed enlarged right lateral rectus muscle (measuring upto 7.5 mm in thickness,on left side it measured 2.9 mm in thickness) with normal anterior tendinous insertion &  thickening of posterior tendinous insertion causing crowding at  the apex of orbit with focal intense postcontrast enhancement in the enlarged right lateral rectus muscle (Figure 2a, 2b). MRI Brain was normal.

After clinical evaluation , laboratory  and radiological investigations, diagnosis of idiopathic   orbital inflammation  was considered and treatment was started.  Oral prednisolone in the dose of 60mg/day (body weight-58 kg) was started initially  for two weeks and dramatic improvement in  symptoms  was noted. Ocular pain was relieved, ptosis in right eye  was improved, abduction was almost full and  slight improvement in elevation right eye was also seen. There was no diplopia on dextroversion, but was present on elevation. After two weeks  dose of oral prednisolone was  decreased to 50mg/day and then tapered slowly later on over two months. After one month of treatment patient,s eyes were almost looking normal except for mild limitation of elevation and  mild diplopia on elevation (Figure 3a,3b,3c). Patient was on weekly follow-up for the first month  and then biweekly  for  the next one month and subsequent follow-up was advised if  patient had symptoms and  risk of recurrence of disease was also explained to her. Patient recovered completely after ten weeks of treatment.

Orbital pseudotumor is not a single entity but rather a spectrum of idiopathic orbital inflammations, excluding infectious, neoplastic, and systemic inflammatory or immunological etiologies.² The term ‘orbital pseudotumor’ was first coined by Birch-Hirschfeld in 1905 to include all the non-specific  or idiopathic obital inflammatory syndromes (IOIS). IOIS is the third most common orbital disease after thyroid orbitopathy and lymphoproliferative disorders.⁴ It represents approximately five to eight percent of all orbital masses.⁵ Disease usually occurs in adults, but may also affect  children.⁶ There is higher incidence of bilateral orbital involvement in children.⁷ Peak incidence is seen predominant typically in the middle-aged persons and there is no sex predilection.⁸ The disease has been reported in all ethnic groups around the globe.⁹

This entity has been further divided into localised and diffuse type. The localized type of idiopathic orbital inflammation was further subdivided into myositis, periscleritis, perineuritis and dacryoadenitis. In orbital myositis, the inflammatory process may involve one or more extraocular muscles.¹⁰ Usually monocular involvement is there, but it could be bilateral also with involvement of one or more muscles in both orbits.¹¹

The clinical course of IOIS ranges from mild and self-limiting to devastating orbital sclerosis with blindness. Disease relapse is common. The clinical presentation of the disorder may be acute, subacute or chronic. The lesion is most commonly restricted to the orbit; however, extension into adjacent retro-orbital structures is also known. The cause of idiopathic orbital inflammation is unknown. Neoplastic, infectious, and systemic inflammatory or immunological syndromes must be excluded. The differential diagnosis of IOIS include Thyroid- associated orbitopathy, Sarcoidosis, Wegener’s granulomatosis, Tolosa-Hunt syndrome, Lymphoproliferative orbital disease, Metastatic orbital disease and Orbital cellulitis. The  laboratory investigations advised in these cases include Complete blood count, sedimentation rate, electrolytes, thyroid function tests, antinuclear antibodies, antineutrophil cytoplasmic antibodies, angiotensin converting enzyme level and rheumatoid factor etc.

No single laboratory test is available to diagnose IOIS. The diagnosis is based on the clinical picture and verification of enlargement of extraocular muscle by orbital imaging (CT& MRI), as well as on the exclusion of any specific disease. Biopsy is not indicated in all cases and should be reserved for the cases with an atypical course⁶ or cases suspicious for an orbital malignancy or when a poor or equivocal response to corticosteroids is seen.

Corticosteroids are the mainstay of therapy, inducing a rapid and dramatic resolution of symptoms within few days after  starting treatment.^12,13  The prompt response to steroids is critical also in establishing the diagnosis of idiopathic orbital inflammation, as other conditions are not expected to exhibit such a rapid and dramatic response.¹⁴ As per literature it is recommended  that oral prednisone  should be initially  used at doses of 60 to 80mg per day over two to three weeks.¹⁴  Then, steroids should be tapered slowly, usually  over six  weeks to  three months,in order to prevent exacerbation or recurrence of  inflammation. The adjunctive use of  immunomodulatory agents or radiotherapy must be reserved for selected recalcitrant cases.¹⁵ This patient had complete ptosis with limitation of movements of abduction and elevation. The lateral rectus was markedly enlarged and showed postcontrast enhancement presumably because of myositis. Oculomotor nerve divides in the anterior cavernous sinus and the superior and inferior division enters the orbit through  the superior orbital fissure. The superior division of third nerve was involved in the inflammatory process which was well corroborated by the MRI  findings  of crowding at the apex of orbit. The involvement of superior division of third nerve lead to complete ptosis and limitation of elevation while involvement of lateral rectus caused restriction of abduction. The patient improved as the inflammation was controlled by the use of oral  corticosteroids.