Idiopathic inflammatory myopathies encompass a group of chronic, autoimmune conditions that primarily impact the proximal muscles. Various diagnostic and classification criteria have been proposed for myositis, incorporating diverse elements such as clinical presentation, laboratory tests including myositis-specific antibodies, electromyography (EMG), muscle biopsy, and muscle MRI [19, 20].

Our study revealed that in the adult-onset group of patients, there was a predominance of females, with dermatomyositis being the most common subtype. This finding aligns with the findings from the EuroMyositis Registry in 2017, which also reported a high prevalence of dermatomyositis and a predominance of female patients (69%). Conversely, the juvenile-onset group in the study showed a predominance of males, with overlap myositis being the most common subtype, which is different from the findings of Tansley and colleagues in 2017, who reported that dermatomyositis was the most common subtype in the juvenile cohort, with a predominance of female patients [21, 22].

One of the mentioned findings in a review carried out by Fernandez and colleagues was that patients diagnosed with IMNM have the greatest elevation in muscle enzyme levels among other forms of myositis, which is consistent with our results (Table 3) [23].

In our study, more than half of the tested patients (56%) were seronegative, potentially due to the presence of untested or novel unidentified antibodies, as suggested by Betteridge and McHugh (2016). In the juvenile-onset group, 44% of patients exhibited positive autoantibodies, 54% of whom had myositis-specific antibodies. This is comparable to the findings of Tansley and colleagues., who identified autoantibodies in 60% of the juvenile-onset cohort within a large British sample, with a similar MSA incidence of 49% [20, 22].

Similar methodology for antibody testing was not found in Middle Eastern studies but was partly related to a 2020 study in India, which included 250 IIM patients (both adults and children) and found myositis autoantibodies (MSAs/MAAs) in 59.2% of patients, with 60.7% in adults and 50% in juvenile IIMs. The ARS subgroup was the most common in the adult group, and anti-Jo-1 was the most common type of MSA, followed by anti-Mi2, which is different from our results in which anti-HMGCR was the most frequently encountered antibody, followed by anti-Ku and anti-Ro52 in our adult group, yet their patients were not tested for anti-HMGCR [24].

Studies on inflammatory myositis in Egypt are limited. One notable study by EL Sherif (2020) on immune-mediated necrotizing myopathy included 18 patients, 83% of whom were seropositive. In the Middle East, research is sparse. A study performed in the year 2023 in Saudi Arabia reviewed 26 patient records over 12 years, focusing on clinical and serological results, specifically anti-Jo-1 antibody results, and identified dermatomyositis as the most common subtype. Similarly, Chatti and colleagues in 2023 conducted a 21-year retrospective study in Tunisia involving 85 idiopathic inflammatory myopathy patients, of which 46 were classified as having dermatomyositis. This study reviewed epidemiological, clinical, and laboratory data, revealing MSAs in 16 patients and treatment responses. In Morocco, a retrospective study over 15 years involving 14 patients focused on clinical, laboratory, and muscle biopsy data, although autoantibodies were not tested [25,26,27,28].

In our studied IMNM subtype, the total number of anti-HMGCRRs was greater than that of anti-SRP; in the adult group, anti-HMGCR antibodies were present in 9% of the total cases, surpassing the prevalence of anti-SRP antibodies, which were found in 2% of the cases. Conversely, in the juvenile-onset group, the prevalence was reversed, with anti-SRP antibodies being more common. This finding is consistent with the results of Tansley and colleagues study on autoantibodies in juvenile-onset myositis, where anti-SRP antibodies were detected in 2% of the patients, and anti-HMGCR antibodies were identified in 1% of the patients. Additionally, in the 2020 El Sheriff study on IMNM patients in Egypt, the number of anti-SRP (45%) patients was greater than that of those who tested positive for anti-HMGCR (33%) [22, 25].

In our patients, pain was reported more often in the IMNM (n = 4) and dermatomyositis (n = 4) subtypes, while skin manifestations and bulbar and respiratory manifestations were highest in the dermatomyositis subtype (Table 3). The presence of myalgia has been previously studied and linked to disease activity and outcome, as concluded by Pillai and colleagues in 2024, who examined 50 myositis patients for the presence and degree of pain longitudinally over a period of 6 months; however, this was not correlated with different IIM subtypes [29].

We included 5 patients in our study, two with juvenile onset and 3 with adult onset with the coexistence of antibodies of different subtypes. Anti-SRP and anti-Ku were the most common in this group, each occurring in 3 patients, and both were detected in two patients (Table 4). This was studied by Huang and colleagues, who performed additional immune assays to confirm double-positive and false-positive cases. Although the coexistence of more than one MSA is rare, it still exists. Additionally, the clinical features tend to skew to one subtype instead of a mixed phenotype [30]. In a 2023 study by Zheng and colleagues, three patients were shown to have both anti-SRP and other antibodies, including anti-TIF1-γ, anti-Jo1, and anti-EJ. The study concluded that this coexistence led to diverse clinical symptoms and outcomes, primarily driven by one of the myositis-specific antibodies or through interactions in a complex syndrome, thereby broadening the clinical spectrum of idiopathic inflammatory myopathy. Additionally, three patients were identified with coexisting anti-SRP and other antibodies (PL-7/12, anti-Ku, Jo-1, PM-Scl75, and MDA5). These patients exhibited varying clinical severities; one patient was wheelchair-bound at the time of diagnosis with respiratory muscle involvement, while the other two patients remained ambulatory [31].

The MRI findings of our patients who presented within the first year of onset showed normal findings or edema with no fat replacement. Patients who were investigated one year after onset showed variable degrees of muscle fat infiltration (Fig. 4). It has been shown recently that in all types of myositis, including IMNM, fatty replacement can begin early after disease onset, suggesting that early diagnosis and initiation of therapy may help to decrease long-term disability [23] this can be seen in MR images from our study that are shown in Fig. 5. Numerous publications have discussed MRI findings in immune-mediated necrotizing myopathy in relation to muscle involvement and pre- and posttreatment observations. For instance, Mohassel and colleagues (2019) assessed six patients with anti-HMGCR antibodies using MRI before and after treatment to monitor disease remission. Despite these studies, the relationship between the duration of IIM at diagnosis and MRI findings remains poorly documented [32].

Our MRI findings in the IMNM group concurred with the fatty infiltration pattern, but posterior thigh muscles were more frequently affected by edema (Table 4), which partly concurs with the findings of the 255th ENMC workshop (2022) on muscle imaging in IIM, which described a suggested MRI pattern in IMNM as edema involving proximal muscles, including the anterior compartment of thigh muscles, while fatty replacement predominantly affected posterior and medial muscle groups; however, they concluded that there is no distinctive pattern for IMNM [14].