71-Year-Old Man With Subacute Forearm Pain Associated With Numbness and Tingling

HISTORY AND PHYSICAL EXAMINATION A 71-yr-old man presented to orthopedic hand surgery clinic with complaints of right hand paresthesias and pain for 1 mo. He reported numbness in all fingers other than the little finger, and symptoms were affecting sleep and aggravated by wrist splint use. Physical exam was notable for volar midforearm and first carpometacarpal (CMC) joint tenderness, with pain during CMC axial grind testing. He had a positive Tinel’s sign at the right wrist, a positive carpal compression test, and endorsed decreased light touch sensation in a median nerve distribution. The patient otherwise had intact strength throughout the thumb, could make a composite fist, and had intact sensation in the radial and ulnar nerve distributions. At 1-mo follow-up, the patient reported worsening symptoms, with the pain, numbness, and tingling now originating from a point halfway along the right volar forearm and radiating into the right fingers. On exam, he continued to demonstrate a positive Tinel’s sign at the right wrist. Light touch sensation was diminished in the first through third digits but was intact in the radial and ulnar nerve distributions. Of note, the point of maximum positive Tinel’s sign was now approximately 8 centimeters proximal to the transverse wrist crease along the path of the median nerve. He also continued to have positive carpal compression test and negative Tinel’s sign at the right elbow. TRANSITIONAL QUESTION Given this patient’s history and exam, what differential diagnoses should be considered as the cause of his symptoms? DIFFERENTIAL DIAGNOSIS Given positive Tinel’s sign at the wrist and forearm, the differential diagnosis includes neuropathies of either the median, radial, or ulnar nerves. Of the three, median neuropathy is the most likely given decreased light touch sensation in the median nerve distribution and positive carpal compression test on physical exam. Intact sensation in the distributions of the radial and ulnar nerves without symptoms during provocative maneuvers on physical exam makes ulnar and radial neuropathies less likely. Other musculoskeletal injuries that are also on the differential, but less likely, include flexor tendon and forearm or carpal bone osseous pathologies. TRANSITIONAL QUESTION What diagnostic measures should be obtained to narrow down the differential diagnosis? DIAGNOSTIC RESULTS Initial diagnostic recommendations were to obtain right wrist radiographs for possible osseous abnormalities and electrodiagnostic testing for evaluation of median nerve compression. Radiographs noted moderate to severe thumb CMC joint degenerative changes. The nerve conduction study demonstrated an abnormal median-D3 sensory nerve action potential, with no response, and an abnormal median compound motor action potential (CMAP), revealing prolonged onset latency but normal amplitude when stimulated at the wrist. However, when stimulated at the elbow and at the axilla, there was 90% decrease in CMAP at both elbow and axilla, suggesting conduction block between the wrist and axilla. An inching study was performed at the wrist to further localize the location of the conduction block. While CMAP amplitudes at 2.5 cm and 5 cm were similar to that of at the wrist, a greater than 90% decrease of amplitude was seen at 7.5 cm proximal to the transverse wrist. These findings collectively suggested evidence of a demyelinating sensorimotor median neuropathy across the right wrist as well as sensorimotor axonal loss and conduction block 7–8 centimeters proximally from the base of the wrist (Table 1). TABLE 1 - Median motor nerve conduction study with inching test Stimulation Site Latency (ms) Amplitude (mV) Wrist 4.9 10.3 2.5 cm proximal to wrist 5 10.4 5 cm proximal to wrist 5.5 7.8 7.5 cm proximal to wrist 6.8 0.2 After his follow-up orthopedic visit, which noted the point of maximum Tinel’s sign to be in the forearm coupled with the electrodiagnostic testing results, the patient was referred to a sports medicine physiatrist for further ultrasonographic evaluation of the right wrist and forearm. Sonography showed the right median nerve to have a bifid component from the carpal tunnel inlet until 7 centimeters proximal to the transverse wrist crease. There were no significant median nerve echotexture abnormalities or obvious compression around the elbow or within the proximal half of the forearm. Approximately 7 centimeters proximal to the transverse wrist crease, hypoechoic fascicular enlargement was noted with a nerve cross-sectional area of 14 mm2. Just proximal to that, a hypoechoic structure was seen coursing radial to ulnar superficially over the nerve terminating at the flexor digitorum superficialis (FDS) tendon (Fig. 1). This structure was thought to either be a vascular leash, a network of small blood vessels forming a tight band, or a fibrous band of connective tissue arising from the FDS muscle.FIGURE 1: Ultrasound images of fascial band compressing median nerve in the right volar midforearm. Sequential images of the median nerve in the volar midforearm from proximal to distal. Black arrow depicts fascial band and white arrow depicts the median nerve. A, Hypoechoic band seen radial to median nerve, which courses superficially and ulnarly (B) and (C) until terminating at the flexor digitorum superficialis tendon (D). In (D) can also appreciate hypoechoic fascicular enlargement, which is just distal to area of compression.Upon completion of the diagnostic testing, the final suspected diagnosis was multifocal compression of the median nerve both at the wrist and within the volar midforearm. TRANSITIONAL QUESTION Given this diagnosis, what management options are most appropriate for this patient? MANAGEMENT AND OUTCOME Two months after his initial presentation, he returned to clinic after undergoing the above diagnostic ultrasound with no change in symptoms and physical exam despite conservative management with splinting. He thus underwent surgical intervention with right carpal tunnel release and right median nerve exploration/decompression in the forearm. During the procedure, the median nerve was confirmed to be compressed at the level of the carpal tunnel and surrounded by chronic fibrous tissue, and thus the nerve was decompressed in this region. The median nerve was also confirmed to be bifid at the level of the transverse crease of the wrist, and the nerve was noted to bifurcate approximately 8 centimeters proximal to the wrist crease. Just proximal to this bifurcation, a fascial band arising from the fibers of the FDS and crossing superficial to the median nerve was noted to be focally compressing the median nerve, consistent with the area of most significant positive Tinel’s sign from the physical exam. The fascial band was thus dissected free and transected. Two weeks after surgery, the patient reported resolution of his pain that had radiated from the right midforearm down to the distal extremity. Physical exam also confirmed symmetric sensation in the median and ulnar distributions of the right hand via light touch and pin prick testing. At the second postoperative visit 5 wks after surgery, the patient continued to report resolution of his above-described pain, with physical exam confirming symmetric light touch sensation of the fingers. DISCUSSION This clinical vignette showcases a rare presentation of median neuropathy at the forearm as well as at the wrist in a patient presenting with right hand paresthesias. This case underscores the importance of combining the unique benefits of different diagnostic testing modalities (physical examination, electrodiagnostics, and diagnostic ultrasound) when investigating less common compressive neuropathies of the median nerve proximal to the carpal tunnel. Median neuropathy is most commonly seen at the wrist as carpal tunnel syndrome, in which the median nerve is mechanically compressed among the other components of the carpal tunnel.1 Some studies estimate that approximately 90% of median neuropathy cases are at the wrist, and 10% are more proximal at the forearm and elbow.2 Structures that can compress the median nerve in the forearm include the bicipital aponeurosis, an accessory head of flexor pollicus longus, and fibers of FDS.3,4 Structures that can compress the median nerve at the elbow include a supracondylar process, the two heads of pronator teres, Struthers’ ligament, an enlarged bicipital bursa, and a hypertrophic brachialis muscle.5 The fibers of FDS can form an arch that can anteriorly compress the median nerve in the forearm.3,4 Previous studies have shown that this arch can be present in 30% to 75% of forearms.5,6 It is unclear how often the presence of this fibrous arch leads to median neuropathy symptoms.6 Of note, the arch usually compresses the median nerve proximally in the forearm, around the level of the branching of the anterior interosseous nerve, while our patient in this case study had FDS fibers compressing the median nerve more distally in the forearm, further underscoring the rare presentation of our case study.4–6 While the diagnosis of median neuropathy can usually be made using the history and physical exam, nerve conduction studies (nerve conduction study) and electromyography are helpful in localizing the region of entrapment for median neuropathy. With median neuropathy at the wrist, nerve conduction study would demonstrate prolonged median sensory latencies across the wrist but with normal radial and ulnar latencies.7 Reduced median compound muscle action potentials and sensory nerve action potentials (sensory nerve action potentials) can also be seen.7 CMAP latencies can also be prolonged, and increasing severity of carpal tunnel syndrome is associated with increasing latencies and decreasing amplitudes of median sensory nerve action potentials and CMAPs.8 With median neuropathy at the forearm, electromyography may also show abnormalities in muscles proximal to the carpal tunnel that are innervated by the median nerve (e.g., flexor pollicus longus, second and third digits of flexor digitorum profundus). Abnormalities in electrodiagnostics due to median neuropathy can also be confirmed with ultrasound, including further direct visualization of potential compressive structures in atypical locations. In addition, median neuropathy is associated with nerve edema which presents with enlarged nerve cross sectional area. This can be sonographically visualized with the short axis view of the nerve, and the nerve can also seem more hypoechoic than normal along with loss of fascicular echotexture.7 Splinting is a first-line nonsurgical treatment method for median neuropathy.9 Other conservative management options include physical/occupational therapy focusing on nerve glide exercises, and corticosteroid injections are additional nonoperative adjuncts.9 With regards to oral medications, a 2-wk course of oral prednisone has been shown to have greater therapeutic effect than nonsteroidal anti-inflammatory drugs, but with less therapeutic effect than corticosteroid injection.9 Platelet-rich plasma injection has also been shown to potentially improve functional outcomes in median neuropathy at the wrist.10 For median neuropathy at the wrist, carpal tunnel release and median nerve decompression remains the most definitive surgical treatment option. For median neuropathy at the forearm, surgical decompression of the nerve at the site of focal compression has been shown to have positive outcomes.3 As seen in this case, ultrasonographic investigation can identify structures that can compress the median nerve both at the wrist as well as more proximally in the forearm. Electromyography/nerve conduction study can confirm the diagnosis of median neuropathy, and ultrasonography can corroborate electrodiagnostic findings through visualizing the area of nerve compression, nerve edema, and loss of fascicular echotexture. Thus, it is important for the physiatrist to maintain a broad differential diagnosis when investigating compressive median neuropathy and to consider utilizing ultrasound to scan structures both in the wrist and forearm to evaluate the neuropathy, especially given the speed and relative low cost of ultrasonography. Note: This study conforms to all RFS CARE guidelines and reports the required information accordingly (see Supplementary Checklist, https://links.lww.com/PHM/C731)