In this revision, we will try to address the entrapment neuropathies of the median nerve, from a clinical and practical approach, so as the family physicians or non-specialist practitioners can know more about these pathologies. Despite Carpal Tunnel Syndrome (CTS) is by far the most common entrapment neuropathy, we should know that not all the pains or paresthesias in the volar side of the hand or forearm are due to CTS. We will deliberately oid too many anatomic data or specific treatment details, of limited utility in general practice. Nevertheless, in the references the reader can get much more information. If this paper can clarify several questions regarding the median nerve compression, signs and symptoms, the authors will feel more than happy, as this is our main objective.
Entrapment neuropathies: Usually, peripheral nerves are prone to entrapment when the pass-through areas of fibrous or fibro osseous tunnels. Other factors can influence nerve entrapment at different locations, like local or generalized oedema (tenosynovitis, arthritis, hormonal changes.), space occupying lesions (tumors, hematoma…), accumulation of substances (amyloidosis, mucopolysaccharidosi). Entrapment Neuropathies (EN) are heterogenous conditions due to different underlying pathophysiology, thus producing very different signs and symptoms, depending upon the nerve, level of compression and other causes. The pathophysiology of the compression will give us the clue for the diagnosis and treatment. The definition of EN is varied. A good definition could be: “disorders of the peripheral nerves that are characterized by pain and/or loss of function (sensory and/or motor) as a result of chronic compression of the nerves” [1]. The main objective of this paper is to draw a schematic map to distinguish among these three different places of compression of the Median Nerve (MN) so as not to mistake them. This knowledge is the only way for an early diagnosis, that is always based upon a clinical suspicion. This is crucial because precocious nerve injuries may be reversible, while prolonged ones may be not. This is applicable not only for family physicians/general practitioners but also for specialists.
The median nerve: The MN is a mixed, sensory and motor nerve, innervating areas of the forearm and hand. It trels down the front of the upper arm, across the front of the elbow into the forearm. There it innervates the flexor and pronator muscles. It also supplies innervation to the thenar muscles and lateral two lumbricals in the hand. This is regarding its motor function. The MN trels through the mid forearm (as its name, “median”), into the hand through the carpal tunnel, giving sensory function to the palm, more precisely to the thumb, finger, middle and radial side of the ring finger.
Carpal tunnel syndrome (compression of the median nerve at the wrist)
CTS was first described by Sir James Paget in 1854 [2], in a man who developed pain and impaired sensation in the hand, from the trauma of a cord drawn tightly around his wrist. It is by far, the most frequent EN, not only of the MN, but of all the rest of EN taken together. It affects about 2 to 3% of the total population [3], and accounts for more than one half of all the EN. Its pathogenesis is the compression of the MN by the transverse carpal ligament at the wrist. The main symptoms are paresthesias and/or pain in the territory of distribution of the MN (in palmar side, thumb, index, middle fingers and the radial side of the ring finger). These symptoms worsen at night and upon awakening (at night, wrist had been in hyperflexion or hyperextension) [4]. Patients try to shake their hands or rub them (Flick´s syndrome) [5]. Nevertheless, the palm sensation is not completely lost, as the palm is innervated by the palmar cutaneous branch, which does not pass through the carpal tunnel. Therefore, if the palmar sensation is lost, the nerve injury is more proximal to the carpal tunnel. On physical examination, percussion on the MN in the carpal tunnel, elicit a sensation of tingling in the distribution of the MN (Tinel´s sign), as we can see in Figure 1. A provocation test that may help in the diagnosis of CTS, consists in increasing the pressure in the carpal tunnel, for example, if the patient hyperflexes the wrist. In the Phalen´s test, the patient holds his wrists in complete and forced flexion (with the dorsal surfaces of both hands together) for up to one minute. If the patient starts feeling the typical CTS symptomatology (paresthesias over MN distribution in the affected hand), then the test is positive (abnormal). Another provocative test over the carpal tunnel is the carpal compression test (Durkan’s test). The clinician compresses the MN with his own fingers until his nail bed whitens, for 30 seconds, on the patient´s proximal wrist crease. If the patient feels pain or paresthesia in the MN distribution, then the result is positive. When CTS is long term, patients may he weakness in the hand and thenar eminence atrophy. The diagnosis of CTS can be done with Nerve Conduction Studies (NCS) that may show mainly the functionality of the nerve, if demyelination is present. Image techniques can be also be used, above all Ultrasonography (US), or in rare cases Magnetic Resonance Imaging (MRI). Regarding CTS treatment, the most useful treatments are splints, local injections of corticosteroids and decompressive surgery [6,7]. Splints can be prescribed for every patient, local injections for patients with less severe symptoms, and decompressive surgery when the symptoms are longer or more severe, and definitely when there is a thenar eminence atrophy or severely impaired NCS [8,11].
Figure 1: Schematic picture of median nerve compression in the carpal tunnel syndrome. We can also see the area of sensory distribution of the median nerve.Pronator teres syndrome (also called pronator syndrome)
The Pronator Teres Syndrome (PTS) was first described by Henrik Seyffarth in 1951 [12]. Behind the CTS, PTS is by far the next more frequent MN entrapment syndrome. PTS is a rare condition, it accounts for