Radiological Findings

Based on the provided CT, MRI, and PET-CT images combined with the patient’s medical history, the main radiological characteristics include:

• In the CT and MRI sequences, multiple abnormalities can be seen in the muscles surrounding bones. The muscles appear swollen or focally thickened, with poorly defined margins.
• On MRI T1 sequences, the muscle signals in the lesion area are mostly isointense or slightly hyperintense compared to normal muscle. On T2 sequences, there is moderately increased signal, and some areas show internal fibrous septations.
• PET-CT shows areas of elevated radiotracer uptake, indicating markedly increased metabolic activity involving bilateral or multifocal muscle groups. There is also increased metabolism at previously involved mediastinal and testicular sites.
• No significant bony structural destruction is noted, but infiltration of the adjacent soft tissue is observed, with disorganized muscle layers. Local subcutaneous or fascial regions may exhibit linear fatty changes.

Potential Diagnoses

Considering the patient’s history of diffuse large B-cell lymphoma and the current imaging findings, the following potential diagnoses should be considered:

1. Lymphomatous Muscle Metastasis or Recurrence
   Given the known history of advanced diffuse large B-cell lymphoma and the imaging presentation of multifocal muscle infiltration with high metabolic activity, there is a strong suggestion of primary lymphoma recurrence or secondary involvement of muscle tissue.
2. Metastatic Muscle Involvement from Other Malignant Tumors
   Although lymphoma is the primary concern, other malignant tumors (e.g., sarcomas or metastatic carcinomas) could involve muscles. Imaging findings may be similar, but given the patient’s previous favorable response to chemotherapy, lymphoma recurrence remains the priority consideration.
3. Infectious or Inflammatory Lesions
   Such as myositis or abscess. These can also present with muscle edema or enhancement on imaging, but typically show more pronounced inflammatory features or systemic infection signs. On PET, the metabolic pattern could differ. Based on the patient’s history, this possibility is relatively low.

Final Diagnosis

Based on the following factors, the most likely diagnosis is recurrent diffuse large B-cell lymphoma with secondary muscle involvement:

• The patient’s known history of stage IV diffuse large B-cell lymphoma and previous involvement of the testes and mediastinum.
• The current presentation of burning sensations, numbness in the lower limbs, and foot drop, suggesting neuromuscular involvement.
• PET-CT reveals multiple foci of high metabolic activity within muscles, consistent with lymphoma infiltration.
• The disease pattern is diffuse or multifocal within muscle tissue rather than an isolated soft tissue or skeletal lesion.

If there is any remaining doubt, a pathological biopsy (via aspiration or surgical biopsy) is recommended for further confirmation.

Treatment Plan and Rehabilitation

Treatment Strategy

• Chemotherapy and Immunotherapy: For recurrent diffuse large B-cell lymphoma, it is customary to add or switch to a chemotherapy regimen containing rituximab. If the patient’s general condition permits, intensified chemotherapy or combined immunotherapy may be considered.
• Radiation Therapy: For areas with significant tumor burden that affect function or cause severe pain, localized radiotherapy can be considered to reduce disease load and alleviate symptoms.
• Neurological and Pain Management: For patients presenting with foot drop, sensory disturbances, or other neurologic signs, collaboration with neurology and rehabilitation teams is advised. Medications and rehabilitation interventions can help reduce nerve compression or inflammatory reactions.

Rehabilitation and Exercise Prescription

Given muscle impairment and neurological symptoms, an individualized, gradual rehabilitation program is recommended, following the FITT-VP principle:

1. Frequency: Initially, conduct low-intensity rehabilitation sessions 2-3 times per week. Gradually increase to 3-5 times per week as tolerated.
2. Intensity: Begin with minimal resistance or non-weight-bearing exercises such as simple ankle strengthening or straight leg raises. Resistance bands or light weights can be gradually introduced as the patient’s condition improves.
3. Time: Each session should last about 20-30 minutes, including a 5-minute warm-up, 10-15 minutes of main muscle strengthening exercises, and 5-10 minutes of stretching and relaxation.
4. Type: For lower limb strength training, incorporate range of motion exercises (e.g., ankle dorsiflexion exercises) along with balance training (e.g., seated or standing balance drills), and add low-impact aerobic activities (e.g., cycling, swimming) as appropriate.
5. Progression: As dictated by the patient’s condition and tolerance to chemotherapy, progress to moderate-intensity lower limb and core strengthening. Reassess every 2-4 weeks. If symptoms improve and the patient’s endurance allows, training intensity may be incrementally increased.

Precautions:

• Monitor for osteoporosis or muscle fatigue to avoid sudden increases in load.
• During chemotherapy or radiotherapy, fatigue and immunosuppression may occur. Close communication with the attending physician and rehabilitation therapist is essential to adjust exercise intensity promptly.
• If significant pain or worsening of neurologic symptoms occurs, suspend the related exercises and seek medical advice promptly.

Disclaimer

This report is a reference analysis based on the provided medical history and imaging data and does not replace in-person consultation or professional healthcare advice. Specific treatment and rehabilitation plans should be carried out under the guidance of a specialized physician.