Could Weakness in the Left Middle Finger Indicate Trigger Finger?

Weakness in the left middle finger without pain may not necessarily indicate trigger finger?

Hello Doctor: My mother has myasthenia gravis and hyperthyroidism (which has been surgically removed, and she is currently taking medication to supplement potassium).
Recently, she woke up one morning with sudden weakness in her left middle finger, unable to lift it (for example, she cannot raise her middle finger independently while playing the turtle game), but she has no problem applying force downwards.
For instance, when her left palm is facing up and she makes a "5" sign, her middle finger noticeably droops; if a pulse oximeter is clipped to her middle finger, it also droops significantly and cannot support itself.
However, the other fingers on her left hand can exert force and move normally, and there is no numbness or pain in her entire left hand, including the middle finger.
Due to the weakness in her middle finger, the movements of her entire left hand have become uncoordinated.
For example, when washing her face, she cannot press all five fingers simultaneously against her face, nor can she touch her cheek with fingers other than her middle finger first; instead, her middle finger must bend and touch her cheek before the other fingers can follow.
Other actions that she could previously perform smoothly are still possible, but the process has become uncoordinated and awkward.
We took her to her regular follow-up appointment at the neurology department, where the doctor asked about numbness and made her press against his fingers to test her strength.
The doctor said it does not seem like an exacerbation of myasthenia gravis and does not appear to be another neurological disease, but he is unsure why this is happening to her.
We also consulted a neurologist at another clinic who mentioned the possibility of trigger finger.
However, since my mother can bend her middle finger normally, has no numbness or pain, and there are no unusual sounds, it seems that the overall movements of her left hand are just less coordinated.
After researching her symptoms, it does not seem to align with typical trigger finger symptoms.
I would like to ask the doctor if this could be an atypical case of trigger finger, or should we consider other possibilities such as atypical arthritis? Thank you.

Guo Xiaojie, 30~39 year old female. Ask Date: 2024/05/30

Dr. Shen Boquan reply Orthopedics

Hello, if your mother's middle finger is weak and difficult to straighten but can bend normally, it may be necessary to consider whether the extensor tendon is injured or even ruptured.
It would be advisable to consult a hand surgeon.
Wishing you good health.
Best regards, Shen Baiquan.

Reply Date: 2024/05/30

More Info

The symptoms you've described regarding your mother's left middle finger weakness are indeed concerning and warrant a thorough evaluation. While the possibility of trigger finger (stenosing tenosynovitis) has been mentioned, it is essential to consider other potential causes, especially given her medical history of myasthenia gravis and hyperthyroidism.

Trigger finger typically presents with a catching or locking sensation when bending or straightening the affected finger, often accompanied by pain or tenderness at the base of the finger. However, in your mother's case, the absence of pain, the ability to flex the finger normally, and the specific weakness in extending the finger suggest that this may not be a classic case of trigger finger.
The weakness in the left middle finger, particularly the inability to extend it while being able to flex it normally, could indicate a problem with the extensor tendons or the muscles responsible for finger extension. This could be due to several factors:
1. Nerve Compression or Injury: The radial nerve is responsible for extending the fingers. If there is any compression or injury to this nerve, it could lead to weakness in extending the middle finger. This could occur at various points along the nerve pathway, including at the elbow or wrist.

2. Tendon Issues: Although less common, an injury or inflammation of the extensor tendons could lead to weakness in extension. This might not present with pain or locking but could result in a functional deficit.

3. Myasthenia Gravis: Given your mother's history of myasthenia gravis, it is crucial to consider that her symptoms could be related to this condition. Myasthenia gravis can cause fluctuating muscle weakness, and while it typically affects more than one muscle group, it can sometimes present with isolated weakness in specific muscles, including those controlling finger movements.

4. Other Neurological Conditions: While the neurologist has ruled out other significant neurological diseases, it may be worth considering further investigations, such as imaging studies or electromyography (EMG), to assess for any subtle nerve or muscle issues.

5. Arthritis: Although less likely given the specific symptoms, inflammatory conditions like rheumatoid arthritis can affect joint function and may lead to weakness or stiffness in the fingers.

Given these considerations, it would be prudent to follow up with a neurologist or a hand specialist who can perform a detailed physical examination and possibly recommend diagnostic tests such as nerve conduction studies or imaging to evaluate the tendons and joints in the hand.
In summary, while trigger finger is a possibility, the specific presentation of weakness without pain or locking suggests that other conditions should be explored. It is essential to have a comprehensive evaluation to determine the underlying cause of your mother's symptoms and to develop an appropriate treatment plan. Early intervention can often lead to better outcomes, especially in cases involving nerve or tendon issues.

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