I. Imaging Findings

Based on the provided lumbar spine MRI and abdominal CT images, the major features are as follows:

• Lumbar MRI: Some lumbar vertebral bodies (mainly at L3) show low signal on T1-weighted images and high signal on T2- and STIR-weighted images, suggesting abnormal infiltration in the bone marrow. A slight bulge or structural destruction of the vertebral body is observed locally, but no obvious compressive fracture is seen. Abnormal signals are noted in the adjacent paravertebral soft tissue, partially presenting slightly high T2 signal.
• Abdominal CT: Post-liver transplantation changes are noted, and no obvious focal enhancement abnormalities are detected in the liver parenchyma. Multiple enlarged lymph nodes can be seen in the porta hepatis region and around the abdominal aorta (the images show multiple lymph node masses with increased diameters). Some of these nodes surround the abdominal aorta and mesenteric vessels, displaying higher soft tissue density.
• Others: No significant vertebral collapse or extensive abscess-like findings are observed, nor are there clear signs of pathological fractures. However, the possibility of ongoing bony destruction should not be ruled out.

II. Potential Diagnoses

Combining the patient’s past medical history (HIV infection, long-term immunosuppression post-liver transplantation) and clinical presentations (low back pain, weight loss, fatigue, intermittent fever) with the imaging findings (widespread involvement of bone marrow and lymph nodes), the main considerations include:

1. Post-transplant lymphoproliferative disorder (PTLD) or lymphoma: In an immunosuppressed state, especially after organ transplantation requiring long-term immunosuppressive therapy, the incidence of lymphoma or PTLD increases significantly. These conditions may present with multifocal involvement of bone marrow and lymph nodes, typically appearing as low T1 signal and high T2 signal.
2. Metastatic cancer: If a primary malignancy exists elsewhere, bone marrow infiltration and lymph node metastasis could also occur. However, the most prominent risk factor remains lymphoproliferative disease associated with immunosuppression.
3. Infectious lesions (e.g., tuberculosis or fungal infections): In patients with HIV positivity and long-term immunosuppression, skeletal infection or spondylitis (such as spinal tuberculosis, bacterial, or fungal infections) must be considered. However, these typically show more pronounced disc destruction and paravertebral abscess with characteristic imaging features. In this case, no obvious abscess or distinct intervertebral disc damage is observed.

III. Final Diagnosis

Considering the patient’s age, clinical features (low back pain, weight loss, fever), immunological status (HIV infection, liver transplantation, long-term immunosuppressive therapy), and imaging findings indicating extensive bone marrow and lymph node involvement, the most likely diagnosis is post-transplant lymphoproliferative disorder (PTLD), i.e., lymphoma.

Since a definitive diagnosis requires pathological confirmation, it is recommended to perform a biopsy of suspicious bone or lymph node lesions to determine the pathological type and immunophenotype, which will guide subsequent treatment.

IV. Treatment Plan and Rehabilitation

1. Treatment Plan

• Reducing immunosuppression: In patients who develop lymphoproliferative disorders post-organ transplantation, it is often necessary to reduce immunosuppressive medications under specialist guidance to enhance the body’s immunosurveillance against tumor cells.
• Chemotherapy: For confirmed PTLD or lymphoma, standard chemotherapy regimens (e.g., CHOP, R-CHOP, or ABVD) may be used, depending on the specific subtype. Throughout the treatment, it is essential to closely monitor infection risk, liver function, and blood counts, given the patient’s immunocompromised status.
• Supportive therapy: This entails nutritional support, anti-infective therapy when necessary, and symptomatic treatments (e.g., pain relief, correction of anemia, and electrolyte balance maintenance).

2. Rehabilitation and Exercise Prescription

During treatment, considering the patient’s overall condition (immunosuppression, possible fatigue, and reduced blood counts during chemotherapy), an individualized and gradual rehabilitation plan should be developed:

1. Initial Phase:
   • Focus on basic joint mobility and mild muscle strengthening exercises, 10-15 minutes per session, 3-5 times per week.
   • Perform exercises beside the bed or while seated, avoiding vigorous movements. Light walking may be initiated if tolerated.
2. Intermediate Phase:
   • When the patient’s condition has stabilized and pain subsides, gradually increase exercise intensity to a moderate level, such as extending walking sessions to 20-30 minutes or adding simple resistance training.
   • Given the patient’s bone density and cardiorespiratory status, avoid high-impact exercises or those with a high risk of falls (e.g., slow walking on flat surfaces, upper-limb exercises with resistance bands).
3. Advanced and Maintenance Phase:
   • With continued improvement, transition to aerobic exercises (e.g., cycling, swimming, or other low-impact exercises) or moderate-intensity strength training for 20-40 minutes per session, 3-5 times per week.
   • Regularly monitor bone density and blood counts to prevent excessive loading or fatigue.

The FITT-VP principle (Frequency, Intensity, Time, Type, Volume, and Progression) should be carefully adapted to the patient’s bone status, immunological condition, and cardiovascular function, ensuring safety and gradual progression.

V. Disclaimer

This report provides a reference analysis based on available imaging data and clinical information. It does not replace in-person consultation or professional medical advice. If you have any questions or if your symptoms worsen, please consult a hospital promptly for further evaluation and treatment.