We define “neuromuscular mimic” as any musculoskeletal condition that presents with pain and apparent weakness, and can mimic a neuromuscular etiology such as radiculopathy or entrapment neuropathy. “Limb pain” is a common reason for referral to the clinic and EMG laboratory and the identification of the underlying pain generator is often challenging. For example, in two series of patients referred for electrodiagnostic testing for suspected cervical or lumbosacral radiculopathy, the prevalence of musculoskeletal disorders was 42% and 32%, respectively.1,2 Thus, musculoskeletal disorders are common in patients suspected of having a radiculopathy. They can mimic radiculopathy or coexist with it in many individuals.1,2 Importantly, neuromuscular mimics can often be diagnosed quickly at the bedside and are eminently treatable. Their prompt recognition may avoid unnecessary and expensive diagnostic procedures and result in more efficient clinical practice. It is common for physicians from many specialties to be unfamiliar with recognizing these conditions.3
In this chapter, we will describe the most common mimics of radiculopathy and neuropathy in the upper and lower limbs (Table 36-1). We will not perform an exhaustive review of these pathologies. Rather, this chapter will serve as an entry point for physicians with minimal musculoskeletal training with the goal of providing them with time-efficient and resource-efficient tools to screen for these common conditions in their busy daily practice.
A few key “pearls” are worth remembering when performing a musculoskeletal examination. First, it is important to check the bilateral limbs for side-to-side comparison, starting from the noninvolved side first, whenever possible. If the test maneuver elicits pain, one needs to ask the patient whether the elicited pain is the same that he/she has been experiencing. This is important in order to avoid overcalling pathology as musculoskeletal examination maneuvers can trigger some discomfort even in healthy individuals, particularly if palpation and provocative tests are performed too vigorously. Finally, when assessing whether the maneuver reproduces the patient’s chief complaint, it is very helpful to look for the “wince sign,” with the patient blinking and grimacing as the pain is reproduced.
TOP MIMICS IN THE UPPER LIMBS
Supraspinatus tendinopathy is a common cause of shoulder pain and can mimic C5/6/7 radiculopathy.
The rotator cuff consists of four muscles that are responsible for securing the arm into the glenohumeral (shoulder) joint. These muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis. The tendon most commonly injured within the rotator cuff is the supraspinatus.4 Risk factors include older age, repetitive overhead activity, whether work- or sport-related, anatomic variants, instability of the glenohumeral joint, and periscapular muscle weakness and imbalance.5–7 The latter are common in people with underlying neurologic diseases.
Patients complain of shoulder pain that is aggravated by arm movement, especially overhead. Painful daily activities may include putting on a shirt or brushing hair. The pain may be localized to the deltoid area, but may also radiate upward toward the neck or distally down the arm, thus mimicking cervical radiculopathy, most often in a C5–C7 distribution. Often, patients have difficulty sleeping on the side of the affected shoulder due to pain.
Shoulder examination includes inspection, range of motion (ROM), strength testing, palpation, and special tests.8 With long-standing rotator cuff tendinopathy, inspection may reveal atrophy of the supra- and infraspinatus muscles. ROM above 90 degrees of abduction, either actively or passively, is often painful. Active ROM may be limited by pain, but passive ROM is preserved. There may be tenderness to palpation over the affected muscles or focal subacromial tenderness at the posterolateral border of the acromion. Pain may also be elicited by one of the many special tests that are available to examine the shoulder.8,9 A simple and sensitive screening test for supraspinatus tendinopathy is the Hawkins test (Fig. 36-1). Reduced passive ROM and weakness with resisted abduction and/or external rotation suggest the presence of adhesive capsulitis and rotator cuff tear, respectively. Musculoskeletal ultrasound and magnetic resonance imaging (MRI) can be considered if further investigation and confirmation of the etiology are desired.10
Hawkins test. Correct positioning is important to perform the test. The patient forward flexes the arm to 90 degrees (A) and the examiner flexes the elbow to 90 degrees (B). The examiner then forcibly internally rotates the shoulder (C). The maneuver drives the greater tuberosity of the humerus farther under the coracoacromial ligament. Pain with this maneuver is considered positive for impingement of the supraspinatus tendon under the acromion.
Conservative treatment for supraspinatus tendinopathy includes rest, activity modification, ice, nonsteroidal anti-inflammatory drugs (NSAIDs), and physical therapy. Physical therapy is directed to preserving ROM while restoring proper muscle activation and strength balance among the muscles of the rotator cuff.11,12 A subacromial steroid injection may reduce pain and enable earlier participation in ROM exercises and rehabilitation.13 Referral to orthopedics, physiatry, or rheumatology for further diagnostic and therapeutic management is warranted if there is no response to several weeks of conservative management or if additional pathology is suspected.
Biceps tendinopathy is a common cause of anterior shoulder pain and can mimic C5/C6 cervical radiculopathy.
The tendon of the long head of the biceps, with its synovial lining, lies within the bicipital groove which is located in the anterior upper humerus and is bordered laterally by the greater tuberosity and medially by the lesser tuberosity. The bicipital groove is easily palpable in the anterior upper arm when the arm is externally rotated (Fig. 36-2). Tendinopathy occurs where the tendon passes through the bicipital groove and over the head of the humerus just like a rope through a pulley. The underlying pathology may involve inflammation of the tendon and tendon sheath (tendonitis, tenosynovitis) and/or chronic overuse injury and degeneration (tendinosis).14
Yergason test. The long head of the biceps tendon is palpated for tenderness in the bicipital groove, between the greater and lesser tuberosities of the humeral head. Localization of the bicipital groove is aided by internally and externally rotating the shoulder with the elbow flexed at 90 degrees while feeling for the tuberosities.
Affected individuals complain of a deep, throbbing ache in the anterior shoulder. Tenderness is usually localized to the bicipital groove, but may radiate to the deltoid region or downward to the anterolateral arm making it difficult to distinguish from upper cervical radicular pain. The pain often worsens at night, especially if sleeping on the affected side, and may increase with lifting, pulling, or repetitive overhead reaching. The risk of developing biceps tendinopathy increases with age and is higher in people who routinely perform activities that require repetitive overhead movements. Importantly, biceps tendinopathy often coexists with other pathologies of the shoulder, including rotator cuff tendinopathy and tears, as well as intra-articular injuries such as a labral tear.15,16
Clinical diagnosis includes assessing for Yergason test, which is tenderness identified by palpation of the long head of the biceps tendon in the bicipital groove while internally and externally rotating the humerus (Fig. 36-2).17 Another helpful test is the Speed test.18 For the Speed test, the patient is asked to flex the arm (lift upward) against resistance from the examiner with the elbow extended and the forearm fully supinated (Fig. 36-3). The test is considered positive when pain is localized to the bicipital groove, implying biceps tendonitis and/or tenosynovitis. Of note, the Speed test may be positive with other shoulder degenerative pathologies. Ultrasound19 and/or MRI20 are not needed for the diagnosis of biceps tendinopathy, but may be considered in patients who are suspected of having additional concurrent shoulder pathologies or are refractory to treatment.
Conservative treatment is appropriate for most patients with biceps tendinopathy.21,22 Treatment includes rest and activity modification to allow the tendon to heal. Oral or topical NSAIDs and modalities, such as ice therapy, help reduce pain and inflammation. The superficial location of the biceps tendon as it runs through the bicipital groove makes it particularly amenable to ice massage. Patients can be instructed to ice the tender area by directly applying ice to the skin using gentle stroking motions (“ice massage”). The paper cup method is a comfortable, convenient, and inexpensive method of performing ice massage. Water is frozen in a paper cup and ice is exposed by tearing the top rim of paper (Fig. 36-4). Ice is then applied to the affected area multiple times a day until the area is numb, which usually occurs within 5 minutes.
Frozen paper cup for ice therapy. A paper cup is filled with water and placed in a freezer. When the water is frozen, the top of the cup can be peeled away to expose the ice. Ice massage is then performed by placing the cup over the injury in a circular pattern allowing the ice to melt away.
If symptoms do not improve with use of rest, activity modification, NSAIDs, and ice therapy, referral to a musculoskeletal medicine expert (from physiatry, sports medicine or orthopedic surgery) may be considered. Physical therapy is used to improve muscle strength and tendon stability. An ultrasound-guided injection of steroid in the biceps tendon sheath is an option for both diagnostic and therapeutic purposes.23,24 Ultrasound guidance is needed to avoid injecting the tendon with resulting risk of rupture. Surgical intervention is used only in selected patients and includes tenotomy and tenodesis.20,25
Lateral epicondylitis (colloquially known as “tennis elbow”) is a common tendinopathy that presents as lateral elbow pain. Pain may radiate distally along the forearm, mimicking C6 cervical radiculopathy or ulnar neuropathy.
The lateral epicondyle of the humerus is located lateral to the olecranon process and is the origin of the wrist and finger extensors. Overuse and poor mechanics can lead to an overload of the extensor tendons.26,27 The underlying pathology is not inflammatory, but rather degenerative and consists of tendon microtearing.28 Pathology most often involves the extensor carpi radialis brevis, approximately 1–2 cm distal to the attachment to the lateral epicondyle, but can affect the other extensors as well.
In most cases, the pain begins shortly after a period of overuse and slowly worsens over weeks and months. There is usually no specific injury associated with the start of symptoms. The point of maximal pain and tenderness is typically located just distal to the lateral epicondyle over the extensor tendon mass, however pain can extend into the distal forearm mimicking C6 radiculopathy. Pain is exacerbated by arm use, especially repetitive wrist extension and pronation/supination activities. There may be perceived weakness in grip strength. Lateral epicondylitis is most often associated with tennis and other racquet sports. Poor technique including improper backhand, string tension, and grip size are contributing factors.29 However, any activity that places excessive repetitive stress on the lateral forearm musculature can cause this condition.30,31
Clinical diagnosis includes assessing for tenderness by palpation over the lateral epicondyle and 1–2 cm distal to it over the common extensor tendon which usually represents the point of maximal tenderness in lateral epicondylitis. The provocative maneuver or “tennis elbow test” consists of resisted radial wrist extension with the forearm in pronation (Fig. 36-5). The examiner stabilizes the elbow with a thumb over the lateral epicondyle. The test is positive if pain is elicited when the patient makes a fist and extends the wrist against resistance by the examiner. The pain is usually worse with the elbow in extension than with the elbow in flexion. Imaging is generally not needed to diagnose this condition, but a plain x-ray of the elbow may be considered to rule out intra-articular pathology and/or loose body fragments. In addition, an x-ray may reveal calcification over the lateral epicondyle. Ultrasound and MRI may be considered if there is no response to conservative treatment.
Tennis elbow test. The examiner stabilizes the elbow while palpating along the lateral epicondyle. With the elbow pronated and a closed fist, the patient extends the wrist against the examiner’s resistance. The point of maximal tenderness is generally located one fingerbreadth distal to the lateral epicondyle over the extensor tendon mass. The pain is usually worse with the elbow in extension than with the elbow in flexion.
Despite the prevalence of lateral epicondylitis and the availability of different treatment options, only few high-quality clinical trials are available to support evidence-based management algorithms for this condition. Activity modification is an important first step in management and includes correcting training or technique errors such as grip size of the tennis racket when appropriate. Initial conservative management also includes pain control by using a short course of topical or oral NSAIDs32 and ice massage (as described above). Wrist extensor stretching (Fig. 36-6)33 and bracing34 are often helpful. Bracing consists of using a counterforce elbow strap. Elbow or “tennis straps” are placed on the forearm a few centimeters distal to the elbow joint, are easy to use and inexpensive. Counterforce bracing may reduce tendon and muscle strain at the origin of the forearm extensor muscles, thus relieving pain during activities. Physical therapy has been found to be effective in lateral epicondylitis.35,36 Therapy includes progressive isometric and eccentric strengthening and incorporates stretching and modalities as needed. Eccentric exercise occurs when muscles contract while lengthening. Application of this technique for lateral epicondylitis involves contracting the wrist extensors against the resistance of an exercise band.37,38 Steroid injections have also been used to treat “tennis elbow.”39 Their use, however, is controversial.40 Trials have found that corticosteroid injections improve short-term outcomes in lateral epicondylitis, but do not prevent recurrence and may actually lead to worse long-term outcomes.36,41,42
De Quervain syndrome is a common cause of wrist pain and can mimic carpal tunnel syndrome, C6 cervical radiculopathy, and superficial radial sensory neuropathy.
De Quervain syndrome is the most common tenosynovitis of the wrist. It results from inflammation of the fluid-filled sheath (synovium) that surrounds the tendons of the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) in the first dorsal compartment of the wrist. These tendons run over the dorsal aspect of the radial styloid process.
The exact causes of De Quervain syndrome are unclear, but they probably include shear and repetitive microtrauma. Postures where the thumb is held in abduction and extension are considered predisposing factors43,44 although evidence regarding a possible relation with certain occupations is controversial. A systematic review of potential risk factors did not find evidence of an association with specific occupation-related activities.45 Women are affected more than men46 and the syndrome commonly occurs during and after pregnancy, due to hormonal changes and possibly lifting the newborn repetitively in a cradled position thus putting stress on the wrist and thumb. Because of the latter postulated risk factor, De Quervain syndrome is also known as “mother’s wrist.”
Patients with this condition present with insidious onset of pain over the dorsal radial aspect of the wrist which may be accompanied by swelling. The pain may radiate distally into the thumb or proximally along the radial aspect of the forearm. Symptoms are exacerbated by grasping or ulnar deviation of the wrist.
De Quervain syndrome can be easily diagnosed on physical examination. Patients usually have tenderness to palpation over the dorsal radial wrist. Finkelstein test is pathognomonic for the condition (Fig. 36-7). To perform the test, the patient is first asked to wrap the fingers around the thumb. To avoid having tight finger flexor tendons splint and immobilize the wrist, it is helpful to ask the patient to wrap the fingers around the thumb lightly, as if the thumb were an egg. The examiner then ulnarly deviates the wrist. A positive test occurs when the patient experiences sharp and intense pain over the radial styloid process, exactly where the tendon sheath takes its course. De Quervain tenosynovitis is a clinical diagnosis and imaging is not needed.
Conservative treatment includes rest, ice, anti-inflammatory medications (oral or topical), steroid injections, and a thumb spica splint. The splint is worn during the day, but the patient should remove it several times a day to perform gentle ROM exercises to prevent the complications of prolonged immobilization. Iontophoresis can help with inflammation and pain control. Steroid injections are very effective in providing pain relief and have a favorable side effect profile.47 They work best when used in conjunction with a thumb spica splint.48 Ultrasound guidance for steroid injection is recommended to more precisely localize the site of injection.49 Surgery is rarely indicated and carries a small risk of injury to the superficial radial nerve.50
Carpometacarpal (CMC) joint osteoarthritis (OA) (colloquially known as “thumb arthritis”) is a common cause of hand pain and can mimic carpal tunnel syndrome.
The CMC joint of the thumb connects the trapezium to the first metacarpal bone and plays an important role in the normal functioning of the thumb (Fig. 36-8). Degenerative changes in this joint result in “thumb arthritis” which can cause severe hand pain, swelling, decreased ROM, and reduced grip strength.51 Pain and swelling occur at the base of the thumb. The discomfort is exacerbated by activities that involve using the thumb to apply force or grasping an object. Thumb arthritis can make it difficult to perform simple household tasks, such as opening jars, pulling a zipper, and turning doorknobs.52 Patients may complain of reduced grip strength.52
Thumb osteoarthritis. The location of the first CMC joint at the base of the thumb is demonstrated in the figure. The grind test is performed by gripping the metacarpal bone of the thumb, loading it with axial forces to push it against the carpal bone (trapezium), and rotating it in circular motion.
The condition is more common in postmenopausal women.53 Risk factors include genetic predisposition,54 history of prior trauma to the joint, occupations involving repetitive thumb use,55 history of rheumatoid arthritis or articular hypermobility,56 and the presence of OA in other joints.57,58