The clinical significance of this adverse effect lies in its impact on quality of life and the potential for misdiagnosis. The symptomatology can be severe enough to limit daily activities and may be mistakenly attributed to a primary rheumatic disease, leading to unnecessary long-term immunosuppressive therapy if the temporal link to isotretinoin is not identified. Therefore, a high index of suspicion is crucial for dermatologists, rheumatologists, and primary care physicians alike.

Aim: To compare the effectiveness of High-Intensity Laser Therapy (HILT) in reducing pain intensity, in patients diagnosed with Isotretinoin-Induced Sacroiliitis.

Isotretinoin (13-cis-retinoic acid) is a highly effective retinoid derivative of vitamin A, renowned for its use in the treatment of severe, recalcitrant nodular acne. By significantly reducing sebum production, modulating follicular keratinization, and exerting anti-inflammatory effects, it has proven to be a transformative therapy for patients with conditions unresponsive to conventional treatments. However, its potent biological activity is accompanied by a well-documented and diverse profile of adverse effects, ranging from common mucocutaneous symptoms like xerosis and cheilitis to more serious concerns such as teratogenicity, psychiatric effects, and musculoskeletal complaints.

Among these musculoskeletal adverse events, sacroiliitis-the inflammation of one or both sacroiliac (SI) joints-has emerged as a significant, though potentially underrecognized, clinical entity. The sacroiliac joints, which connect the sacrum to the iliac bones of the pelvis, are a primary site for inflammatory processes seen in spondyloarthropathies (SpA) such as ankylosing spondylitis. The presentation of Isotretinoin-induced sacroiliitis often mirrors that of these idiopathic conditions, characterized by insidious-onset lower back pain, buttock pain, and stiffness that may improve with activity and worsen with rest. Morning stiffness is a common feature, and pain can often be referred to the groin or posterior thigh.

The pathophysiological mechanism linking isotretinoin to sacroiliitis remains incompletely elucidated but is a subject of active investigation. Retinoids are known to modulate the immune system, influencing the differentiation and proliferation of various immune cells. It is hypothesized that isotretinoin may disrupt the delicate balance between pro-inflammatory and anti-inflammatory cytokines, potentially triggering an inflammatory cascade in genetically predisposed individuals. This theory is supported by the observation that symptoms often resolve upon discontinuation of the drug and may recur upon re-challenge, satisfying important criteria for a causal relationship.

The clinical significance of this adverse effect lies in its impact on quality of life and the potential for misdiagnosis. The symptomatology can be severe enough to limit daily activities and may be mistakenly attributed to a primary rheumatic disease, leading to unnecessary long-term immunosuppressive therapy if the temporal link to isotretinoin is not identified. Therefore, a high index of suspicion is crucial for dermatologists, rheumatologists, and primary care physicians alike.

Aim: To compare the effectiveness of High-Intensity Laser Therapy (HILT) in reducing pain intensity, in patients diagnosed with Isotretinoin-Induced Sacroiliitis.

Secondary Objectives:

• To assess and compare the improvement in functional status and quality of life between the two intervention groups using validated questionnaires.
• To evaluate and compare the reduction in disease activity and inflammatory symptoms (e.g., morning stiffness, night pain) between the groups.
• To measure and compare the improvement in spinal mobility and specific sacroiliac joint provocation tests.
• To monitor the safety and adverse event profile of HILT in this patient population.

Study Design:

A single-center, prospective, randomized, controlled, parallel-group trial with a 1:1 allocation ratio. The outcome assessor will be blinded to the treatment allocation (assessor-blinded). The physiotherapist administering the therapy and participants and cannot be blinded due to the nature of the interventions.

Inclusion Criteria:

• Aged between 18 and 35 years.
• Receiving a stable dose of oral isotretinoin (e.g., 0.3-0.5 mg/kg/day) for at least one month.
• Diagnosis of sacroiliitis based on: Clinical symptoms: Persistent (≥4 weeks) lower back/buttock pain, morning stiffness >30 minutes, improvement with exercise. Positive physical findings: At least two positive sacroiliac joint provocation tests (e.g., FABER/Patrick's test, Gaenslen's test, Compression/Distraction test). Radiological confirmation (MRI): Active inflammation (bone marrow edema) on Short-Tau Inversion Recovery (STIR) sequences in one or both sacroiliac joints.
• A baseline pain intensity of ≥4 on the Visual Analog Scale (VAS 0-10 cm).

Exclusion Criteria:

• ankylosing spondylitis or other seronegative spondyloarthritis
• the presence of pregnancy
• the presence of any cancer
• the presence of multiple sclerosis

No individual participant data will be shared. The investigators will publish the results in academic journals.

The outcome assessor will be blinded to the treatment allocation (assessor-blinded). The physiotherapist administering the therapy and participants and cannot be blinded due to the nature of the interventions.