Medical Imaging Analysis Report

I. Imaging Findings

In this fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) examination, patchy areas of increased FDG uptake are observed extensively within the skeletal muscles, mainly involving the shoulder girdle, pelvic girdle, and proximal limb muscles. No obvious focal soft tissue masses or bony destruction are noted. Compared with normal individuals, skeletal muscle FDG uptake is usually significantly lower than that of the liver or blood pool. However, in this case, it is diffusely and abnormally elevated, suggesting the presence of inflammatory or metabolic abnormalities. On chest CT scanning, no definitive neoplastic changes are identified; the pulmonary parenchyma is generally clear, and there is no obvious enlargement of mediastinal or hilar lymph nodes. Only physiological uptake in the heart and aorta is observed. No definite lesions are found in the abdomen or pelvic region.

II. Potential Diagnoses

Given that the patient is a 62-year-old male with progressive proximal muscle weakness, elevated serum creatine kinase (CK), and widespread FDG uptake in the muscles on PET/CT, the following major considerations or differential diagnoses should be taken into account:

• 1. Dermatomyositis (DM): The patient presents with progressive proximal muscle weakness, possibly accompanied by skin manifestations (e.g., rash), and typical laboratory and imaging findings (indicating widespread muscle inflammation). DM is highly suspected. In addition, there is an association between DM and malignancies, which must be ruled out.
• 2. Polymyositis: Similarly characterized by proximal muscle weakness and elevated CK, with imaging often showing diffuse or patchy muscle enhancement. However, cutaneous manifestations are lacking.
• 3. Statin-associated myopathy: Statins can cause myopathy, but a medication history is required and other myopathies must be excluded.
• 4. Malignant tumor metastasis to skeletal muscle or lymphoma: Malignant infiltration of the muscles can also present with increased FDG uptake, but more commonly presents as focal or nodular patterns, often with additional symptoms or relevant clinical evidence.

III. Final Diagnosis

Based on the patient’s progressive proximal muscle weakness, elevated creatine kinase, and PET/CT findings of widespread patchy FDG uptake in skeletal muscles, along with exclusion of recent strenuous exercise or abnormal glucose-insulin status, the most likely diagnosis is: Dermatomyositis (DM).

Because dermatomyositis is associated with various malignancies, comprehensive screening for hidden malignancies is recommended, including chest and abdominal CT and colonoscopy. If any suspicious lesions or clinical symptoms are present, a biopsy may be necessary to rule out undiscovered tumors.

IV. Treatment Plan and Rehabilitation

Treatment Strategy:

• Corticosteroids and Immunosuppressants: Initiate therapy with corticosteroids (e.g., prednisone) to control inflammation. Based on response, combine with immunosuppressants (e.g., methotrexate, azathioprine, or cyclophosphamide) for maintenance therapy.
• Supportive Treatment: Adequate protein and nutritional support, attention to maintaining electrolyte balance.
• Screening and Management of Potential Malignancies: If any suspicious lesion is detected, consult oncology, surgery, or related departments for possible surgery, chemotherapy, or radiotherapy.

Rehabilitation/Exercise Prescription:

• Rehabilitation Principles: As this disease primarily affects proximal muscles, the initial focus is on reducing inflammation and preserving muscle strength. High-intensity exercise should be avoided, with a gradual approach to increase activity.
• FITT-VP Principles:
  • Frequency: 3-5 times per week, adjusted according to the patient’s endurance.
  • Intensity: Low to moderate; avoid abrupt increases in muscle load. Monitor perceived exertion and heart rate.
  • Time: 15-30 minutes per session initially. If tolerated, gradually increase to 30-45 minutes.
  • Type: Low-impact aerobic exercise, such as walking on level or gentle slopes, static or light resistance training.
  • Volume: Incrementally increase total exercise volume based on progress. Multiple shorter sessions may be used to reduce fatigue.
  • Progression: Gradually increase exercise intensity and duration in line with improvements in muscle strength and symptoms. If the patient experiences muscle pain or significant fatigue, adjust or suspend activity accordingly.
• Training Examples:
  • Begin with walking 10-15 minutes per session, 3 times per week, increasing to 30 minutes as tolerated.
  • Under the supervision of a rehabilitation therapist, use low-intensity resistance exercises (e.g., light resistance bands) without placing excessive load on joints or muscles.
  • Incorporate gentle stretching and relaxation exercises before and after activity to maintain range of motion and relieve muscle tension.