## 1 Introduction  
Idiopathic orbital inflammation (IOI) is a benign, non-infectious inflammatory disorder of unknown cause, accounting for 8-10% of orbital mass lesions [1]. Although no universal classification system exists, IOI is typically categorized by the affected orbital region, including anterior, diffuse, apical (posterior), myositis, and darcyoadenitis presentations. Less common forms include periscleritis, perineuritis, and focal masses [2]. IOI can present acutely, sub-acutely, or chronically; it is usually unilateral, though bilateral cases occur in 8-20% of patients. It most commonly affects individuals in their fifth decade of life, regardless of gender, though orbital myositis is more frequent in young women in their third and fourth decades [3]. Anterior IOI primarily affects the globe, conjunctiva, eyelids, nerves, and surrounding muscles, with pain and periorbital swelling being the most common initial symptoms. Other signs may include conjunctival chemosis, restricted eye mobility, and, less frequently, apoptosis, uveitis, papillitis, or exudative retinal detachment. Diffuse IOI presents similar but often more severe symptoms, frequently accompanied by greater proptoresis [4]. Apical (posterior) IOI is less common, but is associated with worse visual outcomes. Typical features include orbital pain, limited eye movement, and visual impairment. Inflammatory lesions in the orbital apex can extend to the cranial cavity, particularly affecting the cavern sinus and middle cranial fossa; in total, 8.8% of cases show such extension [2]. Tolosa-Hunt syndrome, caused by idiopathic granulomatous inflammation in the cavernous sinus or superior orbital fissure, presents with recurrent or fluctuating ophthalmoplegia, visual impairment, and unilateral headache [5].  
Orbital myositis (OM) refers to inflammation of the extraocular muscles (EOMs) and may stem from systemic inflammatory, autoimmune, or infectious conditions; drug reactions; post-streptococcal infections; or paraneoplastic syndromes. Idiopathic orbital myositis (IOM) is the most common form, and is distinct from skeletal polymositis and dermatomyositis [6]. IOM predominantly affects females (1.4:1), especially young adults aged 33-43 years, though it can occur between the ages of 12 and 78 years. Occasional cases during or after pregnancy lack a definitive causal link [7;8]. IOM typically presents with orbital pain worsened by eye movement, double vision, and swelling or redness near the affected muscle. Ptosis, protosis, and, rarely, globe retraction during eye movement may also occur [9]. It usually involves a single muscle (88% of cases), with the medial rectus being most affected, followed by the lateral rectus, inferior rectus, superior rectus, and superior oblique [7]. Multi-muscle involvement and bilateral cases are less frequent (8-20%), though recurrence raises the rate to 50%, often involving different muscles (migratory IOM). In rare cases, optic nerve dysfunction may occur due to muscle compression at the orbital apex [9]. Patterns of motility disturbances include pure paresis (20.5%), mixed paretic and restrictive (34.1%), and pure restrictive (45.5%), as noted in [PERSON]'s review [6]. Prolonged restricted movement may lead to fibrosis and incomplete recovery. Corticoids are the first-line treatment, with most patients improving within 48 h of systemic prednisolone (1 mg/kg/day), which also aids in diagnosis [10;11]. Biopsy is typically considered for cases that fail to respond to corticosteroid treatment [2]. Prompt treatment may help prevent subsequent fibrosis and restrictive strabismus [6].  
This article aims to present a unique case of IOM, which is associated with poorly controlled diabetes and unresponsive to corticosteroids, along with a review of the literature focused on the imaging of the disease.