1. Imaging Findings

Based on the provided MRI images, significant lesions are observed in the left proximal lateral thigh muscle group (primarily involving the vastus lateralis). The specific findings are as follows:

• Abnormal signal within the soft tissue: On T2-weighted or fat-suppressed sequences, local areas of high signal intensity can be seen, suggesting exudation or fluid-related changes.
• Localized swelling of the tissue: The affected area shows blurred margins and visible swelling, consistent with inflammatory reactions or possible abscess formation.
• Partial ring or peripheral enhancement with a central low-density signal, indicating pus or liquefied areas.
• The lesion extends outward toward the skin, and clinically there is skin ulceration with discharge, matching the imaging findings of a deep soft tissue infection.

2. Potential Diagnoses

Considering the patient’s age, clinical symptoms (severe pain, fever, local swelling, purulent discharge), and imaging findings, the main possible diagnoses or differentials include:

1. Bacterial Myositis / Suppurative Myositis (Pyomyositis)
   • Primarily caused by pyogenic bacteria invading the muscle tissue, potentially leading to muscle abscess formation.
   • Patients often present with severe localized pain, fever, swelling, and even ulceration.
   • Common pathogens include Staphylococcus aureus, Streptococcus species, and Pseudomonas aeruginosa.
2. Necrotizing Fasciitis
   • Caused by a variety of bacteria (both aerobic and anaerobic), characterized by extensive necrosis of the fascia and subcutaneous tissue.
   • Clinically, it often progresses rapidly with significant systemic toxicity; if untreated, serious complications may occur.
   • Imaging may show fascial thickening, fluid collections, or gas formation, but in this case, a localized abscess is more likely.
3. Soft Tissue Abscess
   • Results from local infection by bacteria or other pathogens, often presenting with localized swelling, fluctuation, and possible communication with skin ulcers.
   • Bacterial species identification is crucial for differential diagnosis. Traditionally, Staphylococcus and Streptococcus are considered, but Pseudomonas aeruginosa can also be a pathogen in immunocompromised or specific conditions.

3. Final Diagnosis

Considering the patient’s clinical findings (high fever, severe pain in the left proximal vastus lateralis, local swelling with purulent discharge), pathogen culture results (if confirmed as Pseudomonas aeruginosa), and MRI evidence of abscess formation in deep muscle tissue, the most likely diagnosis is:

Pyogenic myositis caused by Pseudomonas aeruginosa in the left vastus lateralis, leading to abscess formation.

If the causative pathogen or other laboratory tests have not been confirmed, further bacterial culture and susceptibility testing are still required.

4. Treatment and Rehabilitation Plan

4.1 Treatment Plan

• Medication: High-dose antibiotics targeting Pseudomonas aeruginosa (such as anti-pseudomonal β-lactams, aminoglycosides, or fluoroquinolones) are preferred. Liver and kidney function should be closely monitored during treatment.
• Surgical Intervention: Since an abscess has formed and purulent discharge is present, abscess drainage or debridement is necessary to thoroughly remove necrotic tissue and exudate, along with local wound care.
• Supportive Therapy: Includes fluid support, nutritional support, and symptomatic treatment (pain relief, antipyretics, etc.), with close monitoring of the patient’s overall condition.

4.2 Rehabilitation Plan

Once the infection and inflammation are under control, rehabilitation can gradually be initiated, including:

1. Acute Phase (post-surgery/early infection control):
   • The main goal is to promote wound healing and reduce swelling and pain.
   • It is recommended to perform gentle passive or assisted active movement of the affected limb (such as small-range flexion and extension of the ankle and knee joints), avoiding excessive weight-bearing.
   • Keep the wound clean and stable with dressings; during training, take care to avoid tension that could reopen the wound.
2. Recovery Phase (infection controlled, wound mostly healed):
   • Gradually increase functional exercises of the affected limb, starting with low-intensity resistance exercises focusing on isometric contraction of the knee extensors (quadriceps).
   • Exercise frequency: 3–4 times per week, 15–20 minutes each time. Intensity can start with body weight assistance for isometric exercises, then gradually add light resistance bands or minimal loads.
   • Enhance core and overall lower limb coordination. If possible, add balance training for the lower extremities.
3. Consolidation Phase (after basic recovery):
   • Depending on personal fitness, gradually increase exercise duration (approximately 30 minutes each session) and intensity (moderate-intensity resistance training), and include aerobic exercises (e.g., cycling, swimming).
   • Continue monitoring wound healing and infection control. Seek immediate medical evaluation if abnormalities (redness, increased pain, etc.) occur.

Throughout the entire rehabilitation process, the wound and affected limb should be closely observed. In cases of slower infection or tissue repair progress, extend the low-intensity exercise phase accordingly.

5. Disclaimer

This analysis report is based solely on the provided imaging and brief medical history for reference only. It cannot replace an in-person consultation or professional medical advice. Specific treatment plans should be tailored to the patient’s actual condition under the guidance of a professional medical team.