Thoracic Outlet Syndrome Testing Sydney | Nerve Conduction Study | East Neurology
Home / Thoracic Outlet Syndrome Testing

Thoracic Outlet Syndrome Testing in Sydney

Specialised nerve conduction studies for neurogenic TOS — including medial antebrachial cutaneous studies. Dr Ron Granot, FRACP, Bondi Junction.

Book Your Test Now

What is Thoracic Outlet Syndrome?

The thoracic outlet is the narrow space between the neck and the arm where nerves of the brachial plexus and the subclavian blood vessels pass between the collarbone and first rib. When something in this space compresses these structures — most often the lower trunk of the brachial plexus (the C8 and T1 nerve roots) — the result is neurogenic thoracic outlet syndrome (TOS).

True neurogenic TOS — with objective signs of nerve injury on NCS and EMG — is uncommon but well-defined. Disputed (non-specific) TOS has typical symptoms without these objective findings and benefits more reliably from conservative care than surgery. Distinguishing these is the central role of electrodiagnostic testing.

Typical Symptoms

Inner Arm Numbness

Numbness or pins and needles along the inner forearm and the little finger side of the hand (C8-T1 dermatomes).

Hand Weakness

Difficulty with fine motor tasks — opening jars, turning keys, buttons. Weak thumb opposition and finger spread.

Hand Wasting

Hollowing of the thenar eminence (base of thumb) — the classical sign of advanced true neurogenic TOS. May be subtle early on.

Activity-Worsened

Symptoms worse with overhead activity (reaching, hanging out washing, hair brushing) and with carrying heavy loads.

Aching Arm Pain

Deep aching pain in the shoulder, arm or hand, often poorly localised. Sometimes worse at night.

Vascular Symptoms

Hand swelling, colour changes, or coldness suggest vascular TOS — a separate problem from neurogenic TOS, evaluated by vascular surgery and imaging.

Differential Diagnosis

TOS symptoms overlap significantly with several more common conditions. NCS distinguishes them.

ConditionDistinguishing featuresNCS signature
Neurogenic TOSLower trunk (C8-T1) pattern. Thenar wasting. Symptoms with overhead activity.Low ulnar SNAP, low MABC SNAP, low median CMAP. EMG denervation in APB, FDI, opponens.
Ulnar neuropathy at elbowNumbness in little + ring fingers only. Elbow flexion worsens. Tinel's sign at cubital tunnel.Slowing across the elbow. Spared MABC SNAP. Spared median.
Carpal tunnel syndromeThumb, index, middle finger numbness. Nocturnal symptoms.Median sensory and motor slowing across wrist. Normal ulnar.
C8 radiculopathyNeck pain often present. Pain extends from neck down arm.Normal SNAPs (lesion is preganglionic). EMG denervation in C8 muscles including paraspinal muscles.
Pancoast tumourSevere pain, weight loss, Horner's syndrome. Red flag.Similar to TOS but with rapid progression. Chest imaging mandatory.

The Specialised TOS Protocol

Routine nerve conduction studies often miss neurogenic TOS because the most sensitive markers — particularly the medial antebrachial cutaneous nerve sensory study — are not routinely included. A targeted TOS protocol assesses:

Ulnar SNAP

Sensory response from the ulnar nerve at the wrist. Reduced in TOS because the lesion is post-ganglionic.

MABC SNAP

Medial antebrachial cutaneous nerve — the most sensitive single test. Reduced or absent in true neurogenic TOS.

Median CMAP

Compound muscle action potential from APB (median-innervated, but C8/T1 root supply). Reduced amplitude in advanced TOS.

Ulnar CMAP

Motor response from first dorsal interosseous and ADM muscles.

Needle EMG

Sampling of APB (median), FDI (ulnar) and opponens pollicis — both median and ulnar innervated thenar muscles confirms a lower brachial plexus lesion.

Comparison Studies

Same studies performed on the asymptomatic side for direct comparison — small side-to-side differences can be diagnostically meaningful.

What to Expect at Your Test

1

Detailed history and examination

Dr Granot reviews the pattern of symptoms — what makes them worse, the distribution of numbness — and examines for thenar wasting, weakness, and provocative manoeuvres (Roos, Adson) understanding their limitations.

2

Specialised NCS protocol

Routine median and ulnar studies plus the targeted TOS battery — including the MABC sensory study that distinguishes TOS from compressive ulnar neuropathy.

3

Needle EMG of hand muscles

Sampling of both median and ulnar thenar muscles to confirm a lower brachial plexus pattern. Cervical paraspinal muscles to exclude C8 radiculopathy.

4

Comparison and conclusion

Side-to-side comparison with the asymptomatic arm. Findings discussed immediately. Formal report and recommendations for further imaging or specialist referral as appropriate.

Frequently Asked Questions

What is thoracic outlet syndrome? +
TOS is compression of nerves or blood vessels passing between the neck and the arm. The testable form is neurogenic TOS — compression of the lower brachial plexus (C8-T1) usually by a cervical rib, fibrous band, or hypertrophied scalene muscles.
Why is TOS difficult to diagnose? +
There are several types — true neurogenic, disputed/non-specific, vascular — with different criteria. True neurogenic TOS is confirmed by characteristic NCS findings and benefits most reliably from surgical decompression.
What is the medial antebrachial cutaneous nerve? +
The MABC is a sensory nerve of the medial cord — particularly sensitive to lower brachial plexus injury, and one of the most useful single tests for neurogenic TOS. Often missed on routine NCS.
Do I need imaging too? +
If NCS confirms neurogenic TOS, plain cervical spine X-ray looks for cervical rib. MRI of the brachial plexus or CT angiography may be added if surgical intervention is considered.
Will I get the results on the day? +
Yes — preliminary findings discussed immediately, formal written report sent to your referring doctor the same day.
What does treatment look like? +
Non-specific TOS — conservative (postural correction, scalene stretching, scapular strengthening). True neurogenic TOS with confirmed electrodiagnostic features and anatomical cause — surgical decompression by a TOS-experienced vascular or thoracic surgeon.

Related: Cubital Tunnel Syndrome · Carpal Tunnel Syndrome · Nerve Pain Diagnosis

Get a Targeted TOS Assessment

Same-day results • Specialised TOS protocol • Medial antebrachial cutaneous studies included

Book Your Nerve Test Now
Call Us02 9388 0615
LocationSuite 301, Bondi Junction
Emailreception@eastneurology.com.au

Last reviewed: 25 May 2026 by Dr Ron Granot, FRACP — Consultant Neurologist, East Neurology, Bondi Junction.

.