Medical Imaging Analysis Report

I. Radiological Findings

Based on the provided forearm MRI images (T2WI/STIR and T1WI), the following findings can be observed:

• In the proximal to mid forearm, within the radial-side deep flexor muscle group (mainly including the flexor pollicis longus muscle group and the radial part of the flexor digitorum profundus), T2WI/STIR shows focal or cord-like hyperintense signal changes.
• In some images, the muscle bellies of the flexor pollicis longus and the radial portion of the flexor digitorum profundus may demonstrate localized increased signal; mild muscle atrophy or fatty infiltration can be observed locally (more prominent on T1WI).
• No significant bony abnormalities or obvious structural destruction of the elbow joint; the joint capsule and articular surfaces appear essentially normal.
• No obvious soft tissue tumor or space-occupying lesion is identified; only a slightly narrowed fat space around the nerve area is noted locally.

II. Potential Diagnoses

Considering a 48-year-old female with forearm pain and flexion dysfunction in the distal interphalangeal (DIP) joint of the index finger and the interphalangeal joint of the thumb, the following differential diagnoses are to be considered:

1. Anterior Interosseous Nerve Syndrome (AIN Syndrome):
   Caused by compression or injury of the anterior interosseous branch of the median nerve, affecting only motor fibers. This can present with weakness in flexing the distal interphalangeal joints of the thumb and index finger, typically manifested by an inability to form the “OK sign.” On imaging, the involved muscles (flexor pollicis longus, radial part of the flexor digitorum profundus, and pronator quadratus) may show hyperintense signals on T2WI. This is the most common potential diagnosis.
2. Tendon structural injury (e.g., partial tear of the flexor pollicis longus or the flexor digitorum profundus tendon of the index finger):
   Partial tendon injuries can lead to similar functional impairments in flexion of the fingers or thumb. However, tendon ruptures typically involve a clear history of trauma or severe pain, and MRI would demonstrate interruption of tendon fiber continuity, which is not fully consistent with this case.
3. More proximal lesion of the median nerve:
   If the median nerve is compressed at a more proximal site, such as at the elbow or a widespread lesion in the proximal forearm, similar finger and thumb dysfunction may occur. However, this is often combined with sensory involvement (which is not clearly present in this case).
4. Other compressive lesions:
   Rare soft tissue tumors or vascular anomalies could cause localized nerve compression, but no obvious space-occupying lesion was found on this MRI.

III. Final Diagnosis

Taking into account the patient’s age, the symptoms (weakness in extending or flexing the distal joints of the thumb and index finger, inability to form the “OK sign”), the MRI findings (localized hyperintense signals on T2WI with partial muscle atrophy), and the absence of notable sensory disturbance, the most likely diagnosis is:

Anterior Interosseous Nerve Syndrome (Kiloh-Nevin Syndrome).

If further confirmation is needed, combining electromyography (EMG) to assess nerve innervation of the affected muscles and ruling out rare tumors or vascular malformations is advised.

IV. Treatment Plan and Rehabilitation

Most AIN syndromes are related to nerve compression or localized inflammation, and often exhibit a degree of spontaneous recovery. Therefore, the treatment strategy generally includes:

• Conservative treatment:
  It is recommended to implement conservative management for at least 8–12 weeks, including physical therapy (such as physiotherapy, ultrasound, or soft tissue mobilization), administration of non-steroidal anti-inflammatory drugs (NSAIDs) to alleviate local inflammation and pain, and reducing external compression or repetitive activities.
• Surgical treatment:
  If there is clear evidence of compression, a local tumor, or another identifiable compressive lesion, or if no significant improvement is noted after 3–6 months of conservative treatment, surgical decompression or exploration can be considered.
• Rehabilitation and exercise prescription:
  For forearm and hand dysfunction, it is recommended to adopt a phased approach to training in order to improve or maintain function of the affected muscle groups:
  1. Initial Phase (Weeks 1–4):
     • Perform light grip training with a soft grip ball: gently squeeze using fingers and thumb, 10–15 repetitions each time, 2–3 sets a day.
     • Practice active forearm pronation and supination exercises, starting with small ranges of motion, 2–3 times per day, 10–15 repetitions each time.
     • Avoid excessive force or prolonged repetitive movements.
  2. Intermediate Phase (Weeks 4–8):
     • Gradually increase resistance training, such as using a grip ball or resistance bands, progressively intensifying the load for the forearm muscles.
     • Focus on precise flexion exercises targeting the flexor pollicis longus and flexor digitorum profundus (e.g., assisted pinch training between thumb and index finger under the guidance of a therapist).
     • Perform these exercises 3–4 times a week for 15–20 minutes each session, progressively increasing intensity.
  3. Late Phase (Weeks 8–12 and beyond):
     • Once symptoms permit or partial function returns, include refined hand coordination and endurance training (e.g., using putty or finger coordination tools).
     • Gradually reintroduce functional exercises based on daily activities, such as various pinch grips between thumb and index finger, in a safe environment.

The FITT-VP principle (Frequency, Intensity, Time, Type, Volume, Progression) should be adjusted in response to the patient’s rehabilitation progress, under the guidance of a professional therapist or physician.