Ulnar Neuropathy at wristElectrophysiological Approach

Dr.Roopchand.PSSenior Resident AcademicDepartment of Neurology.

Introduction:

• Rare than ulnar neuropathy at elbow.• Can mimic early MND.• Good knowledge of local anatomy required.

Anatomy:• Ulnar nerve enters the wrist at Guyons canal.– Proximally pisiform bone– Distally hook of hamate– Floor : transverse carpel ligament, hamate,

triquetrous bone– Roof loosely formed at inlet and thick band of

tissue at outlet – pisiohamate hiatus.– At the hiatus divides in to ulnar sensory branch

and deep palmar motor branch.

Supply:

1. Hypothenar motor: At hiatus – ADM, Opponence digiti minimi, flexor digiti

minimi, palmaris brevis.

2. Superficial sensory br:– Volar 5th and medial 4th digit.

3. Deep palmar motor br:– 3rd and 4th lumbricals, four dorsal and three

palmar interossei, adductor pollicis, flexor pollicis brevis deep head.

Clinical:

• Can be typed according to location of lesion and fibers affected.– Distal deep palmar motor lesion.– Proximal deep palmar motor lesion.– Proximal canal lesion.– Pure sensory lesion (rare).

Most common

Presentation:

• Weakness and atrophy of ulnar intrinsic muscle.

• Thenar and hypothenar wasting can be seen• Benediction hand posture, Forment’s sing,

Wartenberg’s sign can be seen.• Sensory disturbance over volar 5th and medial

4th finger.– Dorsal medial aspect spared.

Etiology:

• Repeated work related trauma.• Wrist fracture.• Ganglion cyst in Guyon’s canal.• Neurofibroma.

Differentials:

• Early MND: – UNW not all C8 T1 muscles affected.

• Ulnar neuropathy at elbow.– Correlating sensory loss.

• C8 T1 radiculopathy• Lower trunk, medial cord brachial

plexopathies.

Electrophysiological evaluation.

Normal Values:

• FDI latency: < 4.5ms• FDI VS ADM Latency comparison: <2ms• Side to side comparison FDI: <1.3ms• 2nd lumbrical Vs ulnat interossei: <0.4ms

Ulnar motor study recording FDI:

• Distal deep palmar br lesion:– Latency and CMAP

amplitude affected.– When compared with

ADM latency – highly s/o UNW

– ADM recordings also affected in more proximal lesions

• >2ms difference significant..

Dorsal cutaneous Sensory study:

• Normal SNAP in UNW.• If abnormal suggests

UNE.

Median Second lumbrical VS Ulnar Int DML:

• Same as Median study in CTS.

• Latency diff > 0.4 significant.

• If there is associated CTS – difficult to interpret.

Wrist and Palm stimulation:

• FDI recorded.• Stimulated 3cm above

the wrist and 4cm distal to distal palmar crease.

• Drop in amplitude or decrease in CV.

• Any CV <37m/s is of localizing value.

Short segment Incremental studies.

• Inching done from 2 to 4 cm above and 4 to 6 cm below distal wrist crease.

• 1 cm intervals.• NL 0.1 to 0.3 ms/cm• Latency >0.5ms – focal

slowing.

• Wrist and palm stimulation showing focal slowing 100% specific.

• Inching is also very sensitive and specific.• In lumbrical-interossei study increasing the cut

off value to 0.7 can eliminate the problem of co existent median neuropathy.

• FDI vs ADM latency comparison is least sensitive.

EMG approach:

• FDI and ADM sampled to look for distal/proximal deep br involvement.

• FDP5 and FCU : to r/o ulnar neuropathy proximal to wrist.

• Radial and Median innervated C8 muscles & lower cervical paraspinal muscles: to r/o radiculopathy.– Abd. Pollicis brevis, flex. Pollicis longus, ext.

indices proprius.

Recommended EMG Protocol for UNW:

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