Brachial plexopathy and upper extremity neuropathies

Brachial plexus Anatomy: 

The brachial plexus is located between the lower neck and axilla, running behind the scalene muscles proximally and behind the bony clavicle and the pectoral muscles distally. 

Roots:  

Trunks: 

The trunks then divide into anterior and posterior divisions

Cords and nerves:

Radial nerve

Median Nerve

Ulnar nerve

Brachial plexus, upper trunk (Erb-Duchenne Palsy):

Brachial plexus, lower trunk (Dejerine-Klumpke's Palsy):

Traumatic plexopathies and time for intervention

Brachial Plexus  EDx Table

Brachial Plexopathy NCS/EMG protocol

Pearl regarding FCR:

Anomalous innervations

The Martin-Gruber anastomosis:

Riche-Cannieu anastomosis is a communication in the palm between the recurrent motor branch of the median nerve and the deep branch of the ulnar nerve. The result is dual innervation of some intrinsic hand muscles such as the first dorsal interosseous, adductor pollicis, and abductor pollicis brevis. "All ulnar hand" results and affects only motor nerves. Stimulating the ulnar nerve at wrist, while recording at thenar results in all motor response.

Accessory deep peroneal nerve: Extensor digitorum brevis muscle is normally innervated by deep peroneal nerve.  In 28% of people (present bilaterally in 57% of these individuals), the superficial peroneal nerve supplies an extension to innervate the lateral slip of EDB muscle, in the form of communicating branch called an accessory peroneal nerve (it travels posterior to the lateral malleolus to innervate the EDB). When present, stimulation at the anterior ankle will result in CMAP that is smaller than when stimulated below the fibular head. Stimulation behind the lateral malleolus will result in a CMAP which is roughly equal to the difference between the anterior ankle and fibular head stimulation sites. 

DDx of withered hand - Wasting of muscles of hand

A LMN lesions is a strong possibility unless there is an arthropathy leading to disuse atrophy.  

C8-T1 involvement.  

Check joint positions in MCP, and ICP joints

Claw hand deformity

Striatal hand of PD

Corticobasal degeneration

Lesions of AHC (C8-T1):  

Root lesion (C8-T1)

Brachial plexus lesions (lower trunk/medial cord):  sensory and motor deficits

Combination of median/ulnar nerve lesions:

http://neuromuscular.wustl.edu/nanatomy/cervanat.htm 

Case Vignette:  

A 26-year-old, right-hand-dominant woman is referred to the EMG lab for electrodiagnostic assessment of left upper extremity pain and numbness.  According to the patient, she has a several year history of intermittent numbness along the medial aspect of her left forearm and hand that is often precipitated by the supine position.  She also reports a 10-year history of aching pain along the medial aspect of her left arm and forearm and that her friend noted that the base of her thumb looked funny.  Her left thenar eminence is severely atrophied, there is weakness of left thumb abduction > thumb tip flexion and index finger extension, as well as diminished sensation along the radial aspect of the left forearm and hand.  

The distribution of pain and tingling along the medial aspect of the arm, forearm, and hand suggest C8 and T1 nerve fiber involvement in the distribution of weakness suggests the supraclavicular localization (e.g., lower plexus or root level).  At this point, the screening sensory NCS can be performed, beginning with the left upper extremity:  NCS (sensory): Median-D2-C6,7 (PkLat: 3.1 ms, SNAP 51 mcV); ulnar-D5-C8 (2.7, 16); superficial radial-C6, 7 (2.2, 59).  The screening sensory NCS appear normal.  However, it is important to assess the relationship of the sensory response amplitudes with each other to avoid missing a relative abnormality.  Notice that the amplitude value of the median response is approximately 2.5 times the lower limit of normal.  The amplitude value of the ulnar response, however, is about 1.25 times the lower limit of normal, and that the amplitude value of the superficial radial response is more than 3 times the lower limit of normal.  Comparison of these values in relation to the cutoff value for normal suggests a possible relative abnormality of the ulnar response.  Thus, the ulnar-D5 NCS should be performed on the contralateral side.  Right ulnar-D5-C8 (2.6, 41.7).  The amplitude value of the contralateral ulnar responses nearly 3 times larger than that of the ipsilateral response, identifying a relative abnormality.  This abnormality indicates an axonal loss process involving the ulnar nerve, the medial cord, or the C8 fibers of the lower plexus.  In this setting, the MABC NCS is performed bilaterally.  Left MABC-T1 (NR).  Right MABC-T1 (2.5, 15.8).The absent MABC shortens the list of potential localization sites to the medial cord of the lower plexus.

Another important feature of these values is the variation in the degree of involvement of 2 abnormal responses-the ulnar response is relatively abnormal and the MABC response is absent.  This suggest that the lesion might be at the APR level and affect the T1 APR to a greater extent than the C8 APR, which is a feature of true neurogenic thoracic outlet syndrome (TN-NOS).   With TN-TOS a fibrocartilaginous band extends from the first thoracic rib to the C7 vertebral body (either to an elongated C7 transverse process or to a rudimentary C7 rib).  This causes the inferior aspect of the brachial plexus to be stretched over the band, producing a traction injury at the APR level or the proximal lower trunk level that affects the more inferior fibers (i.e. the T1 nerve fibers) more than the more superior fibers (i.e. the C8 nerve fibers).

The sensory nerve fibers studied by the MABC NCS emanate from the T1 DRG, whereas those studied by the ulnar-D5 NCS emanate from the C8 DRG.  Thus, disorders involving the T1 APR to a greater extent than the C8 APR or involving the inferior aspect of the lower trunk affect the MABC sensory response to a greater extent than the ulnar sensory response.  At this point, the motor NCS can be performed, adding the bilateral radial-EI, bilateral ulnar-FDI, and the contralateral ulnar-ADM NCS to the routine NCS (for localization and severity assessment).  Left median-APB (wrist): 3.6: 2.2.  Left median-APB (elbow): 2.1, 2.1.  CV: 51.  Right median-APB (wrist): 3.5, 12.4.  Right median-APB (elbow): 12.4.  CV: 52.  Left ulnar-ADM (wrist): 2.7, 12.3.  Left ulnar-ADM (above elbow): 12.1.  CV: 53.  Right ulnar-ADM (wrist): 2.7, 14.1.  CV: 52.  Right ulnar-ADM (above elbow): 14.  CV: 56.  Left ulnar-FDI (wrist): 4.2: 10.1.  Left ulnar-FDI (above elbow): 10.  CV 54.  Right ulnar-FDI (wrist): 4.1, 15.3.  Right ulnar-FDI (above elbow): 15.1.  CV: 54.  Left radial-EI (forearm): 1.6, 2.1.  Left radial-EI (elbow): 2.1.  52.  Right radial-EI (forearm): 1.7, 4.6.  Right radial-EI (elbow): 4.6.  53.  The median motor response is very low in amplitude, indicating a severe axonal loss process.  The 2 ulnar motor responses are normal, but clearly lower than the contralateral side (especially the ulnar-FDI response).  However, they do not meet criteria for relative abnormality (i.e., <50% of the contralateral side).  The amplitude value of the radial motor response is abnormal.  Its involvement excludes medial cord localization.  Thus, at this point, there is an axon loss process involving the lower plexus. 

Similar to the range of severities noted on the sensory NCS, where the MABC response (T1 DRG-derived sensory axons) was affected to a much greater degree than the ulnar response (C8 DRG-derived sensory axons), the median-APB response (T1 > C8) is affected out of proportion to the 2 ulnar responses (C8 > T1).  Again, this is the typical pattern of NCS abnormalities observed in TN-TOS.  At this point, the needle EMG study can be performed, adding muscles in the muscles domain of the lower plexus and determining whether the APB muscle is affected to a greater degree than the other lower plexus innervated muscles (i.e. looking for the same T1 > C8 pattern).

Left APB, FDI, EIA, FPL: Abnormal.  Left APB severely abnormal.  Left PT, biceps brachii, triceps, lower cervicals paraspinals, high thoracic paraspinals and  right APB, FDI, EI, triceps: Normal.

The abnormal muscles are in the muscle domain of the lower plexus with the APB muscle iaffected to a greater degree than the other affected muscles.  The fibrillation potentials were low in amplitude, consistent with a chronic process, as indicated by the presence of long duration MUAPs in the affected muscles.

Electrodiagnostic study impression: Left lower plexopathy (suspect TN-TOS).

Left lower plexopathy is axon loss in nature and severe in degree.  The abnormality is localized to the lower plexus and the pattern of abnormalities indicate that the T1 sensory and motor nerve fibers are affected to a greater extent than the C8 sensory and motor nerve fibers.  This constellation of electrodiagnostic abnormalities is considered essentially pathognomonic of TN-TOS.  Since its severity is slowly progressive disorder it permits reinnervation to keep pace with denervation.  For this reason, it does not respond to conservative therapy and, therefore is treated surgically by a neurosurgeon specializing in brachial plexus disorders.

Pancoast's syndrome

Neoplastic/noneoplastic tumors causing Brachial plexopathies

Classic postoperative paralysis

https://practicalneurology.com/articles/2015-nov-dec/how-to-know-it-when-you-see-it-diagnosing-neuralgic-amyotrophy-parsonage-turner-syndrome/pdf

Hereditary Neuralgic amyotrophy

Some cases of hereditary neuralgic amyotrophy has been linked to SEPT9 gene on chromosome 17q25.3 which is a member of cytoskeleton-related septin family.   It is genetically heterogenous and has been linked to a variation or duplication in the SEPT9 gene in only 55% of affected families.  Presentation is similar to idiopathic neuraglic amyotrophy but with recurrent attacks and autosomal dominant inheritance pattern.   Other distinguishing features include family history, earlier age of onset, higher rate of recurrence, and the presence of dysmorphic features.  

The European CMT Consortium diagnostic guidelines for HNA, supplemented by Alfen et al:

Onset of HNA usually occurs in the 2nd or 3rd decade of life, though earlier or later onset is possible.  HNA can run 2 distinct courses: a relapsing/remitting course with symptom-free intervals or incomplete recovery, characterized by persistent neurologic deficits after repeated attacks in the same limb.  Dysmorphic features include long, narrow face, small mouth, hypotelorism (close-set eyes), shortened palpebral fissures, epincanthal folds, cleft palate, minor syndactyly, circular skin creases, long-nasal bridge, and short stature.  

There is no standardized approach for treatment.  Some case series suggest early corticosteroid therapy or IVIg may benefit in the acute phase of neuralgic amyotrophy.  

https://www.neurology.org/doi/10.1212/WNL.57.11.1963

https://www.researchgate.net/figure/Ten-year-old-male-with-recurrent-hereditary-neuralgic-amyotrophy-HNA-Courtesy-of_fig1_278680338

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1399-0004.2008.01022.x

Neuralgic amyotrophy : Current Opinion in Neurology (lww.com) 

History taking  in NA/PTS:

What went wrong with your arm and when? 

How much did it really hurt in the beginning (on a scale of 0 to10)? 

Did the pain disturb your sleep? 

What did you take for your pain? did it help at all? 

How long did that initial pain score last? 

When did you notice that certain movements or postures became difficult? 

Has moving or using your arm overhead become difficult for you? 

Did you see or feel your shoulder blade protrude? 

Did you notice any tingling or numb sensations? 

Did you have other symptoms like hoarseness or shortness of breath lying down or bending over? 

Was the onset preceded by an infection, surgery, pregnancy or giving birth, stress etc? Course and recovery.

Do you still have pain? If so, is it different from that at onset?  Can you provoke it? How? (stretch sensitive or postexercise muscular).

 Have you noticed any recovery yet? (e.g. is the shoulder blade back against the chest wall at rest etc.)

Are there certain activities in daily life that you cannot do anymore? How about work and sports?  

Have you stopped working / have you tried to work again 

Have you ever had this before? 

Or did you ever have a painless wasting of muscles or a protruding shoulder blade? 

Is there anyone in your family who had something like this? 

Do you or did you have a carpal tunnel syndrome or dropfoot? Anyone in your family? 

Update on Neuralgic Amyotrophy

It is actually an extra plexitis and a peripheral vascular axonal neuropathy.

Check brachialis muscle.  Limited series, pronator quadratus, flexor carpi radialis and flexor pollicis longus.

MRI and ultrasound must include above the elbow as these are common anatomical positions where the median nerve can be affected.

Vascular immunology Mechanism.  There is sudden onset resulting in perineural edema followed by scarring in the healing phase.  The scarring is mostly in the collagen connective tissue supporting the perineurium and this results in fascicular constrictions.

Surgical interventions in the acute and chronic phases. 

Idiopathic brachial neuritis, neuralgic amyotrophy (NA) or Parsonage-Turner syndrome can mimic cervical radiculopathies clinically and should be part of the differential diagnosis for those presenting with limb symptoms, particularly in the shoulder girdle region.  The most commonly involved nerves are the suprascapular, long thoracic, anterior interosseous, and axillary nerves.  More than one nerve may be involved.  Because of the prominent C5-C6 innervated muscle patterns, neuralgic amyotrophy may mimic upper trunk plexopathy or radiculopathy.  Patient with neuralgic amyotrophy give history of shoulder region pain, described as sudden in onset, severe in degree, and transient (typically lasting 1 to 2 weeks); and presence of muscle weakness and wasting in the forequarter region of the body (typical a severe degree, frequently limited to a single muscle or muscle head, and usually becoming apparent when the decrease in pain permits the patient to use the arm).  In addition, majority of patients have an antecedent event known to be associated with neuralgic amyotrophy and a latent period between the trigger and the onset of the pain.

Musculocutaneous Neuropathy

Axillary neuropathy

Radial neuropathy

Wrist drop: Possible Anatomical Locations

Causes of Wrist Drop and Normal Superficial Radial SNAP

Median mononeuropathies

Median neuropathy in the axilla:

Lesions at the ligament of Struthers:

Pronator Teres Syndrome:

Anterior interosseous syndrome:

Carpal tunnel syndrome:  

Carpal tunnel:

Identification of Aberrant Muscle Bellies in the Carpal Tunnel using Sonography - PMC (nih.gov) 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7460039/

DHIS

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3782223/#:~:text=The%20etiology%20of%20DHIS%20is,gangrene%5B1%2D3%5D.

The intrinsic hand muscles including the APB muscle are traditionally known to be innervated by both T1 and C8 nerver oots/segments.  However, current understanding confirms that the principal innervation of APB muscle is the T1 root/segment.  EDx findings supporting predominant T1 root involvement include a low median CMAP amplitude recorded from the APB.  Although the medial brachial and antebrachial cutaneous nerves also shareT1 innervation, their sensory nerve action potentials are preserved inT1 radiculopathy owing to the extraspinal location of the dorsal root ganglion. 

https://www.neurology.org/doi/pdfdirect/10.1212/WNL.0000000000209561

Ulnar neuropathies

Ulnar nerve entrapment sites:


Ulnar nerve entrapment at the elbow (UNE): 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5908985/pdf/WJO-9-65.pdf

Ulnar nerve entrapment at wrist:

Cervical Plexus