Trigger finger at the wrist caused by an intramuscular lipoma within the carpal tunnel: A case report

Abstract

Background: Trigger finger at the wrist, which occurs with finger movement, is an uncommon presentation. Few reports describing cases of trigger finger at the wrist have been published. Thus, we present a case of an intramuscular lipoma arising from an anomalous flexor digitorum muscle belly in a 48-year-old female patient causing painful finger triggering at the wrist and carpal tunnel syndrome (CTS).

Case summary: A 48-year-old woman with complaints of a catching sensation during wrist motion and a progressive tingling sensation on the palmar aspect of the right hand for approximately 2 years was referred to our hospital. Triggering of the index to middle finger was evident with a palpable and audible clunk over the carpal tunnel during passive motion. Tinel's sign was positive over the carpal tunnel of the right wrist with a positive Phalen's test. Nerve conduction studies of the median nerve demonstrated a right CTS. Ultrasound examination revealed a 2.5 cm × 2.0 cm subcutaneous hyperechoic mass with no obvious blood flow at the wrist of the right arm. Surgical excision of the tumor and muscle mass led to a resolution of the patient's symptoms, and any triggering or discomfort disappeared. The patient has had no evidence of recurrence at more than 1 year of follow-up.

Conclusion: Triggering of the fingers at the wrist is rare. It must be noted that there are many possible causes and types of triggering or clicking around the wrist. Accurate diagnosis is mandatory to avoid inaccurate treatment of patients with trigger wrist. During the diagnosis and treatment of CTS, attention should be paid to the variation of tendon tissue in the carpal tunnel, to avoid only focusing on the release of transverse carpal ligament and ignoring the removal of anomalous muscle belly.

Keywords: Case report; Flexor digitorum superficialis; Intramuscular lipoma; Muscle belly; Treatment; Trigger finger.

Figure 1

Operating images of the entire surgical process. A: Preoperatively, there was an intumescence at the distal end of the forearm (orange arrow); B and C: The mass was revealed layer-by-layer during the operation; D: The mass and surrounding fascia were completely removed, and the muscle belly of the flexor digitorum superficialis was abnormally shifted down (orange arrow).

Figure 2

Entrapment symptoms appeared within the carpal tunnel during finger flexion and extension. A: The tumor involved the flexor digitorum superficialis of the index finger in the carpal tunnel; B: In the passive flexion position of the index finger, the mass moved proximally with the flexor digitorum superficialis; C and D: In the extension position of the index finger, the mass moved with the flexor digitorum superficialis and extended into the carpal tunnel. In the overextension position, the mass further moved into the carpal tunnel, extruding the common flexor tendon sheath and the median nerve.

Figure 3

Microscopic observations revealed mature adipocytes and some muscle fiber tissues, with no adipoblasts and abnormal mitotic cells in the tumor. A: Under low magnification (10 ×); B: Under magnification (100 ×); C and D: Under high magnification (200 ×).