Anomalous innervations by;Chaman Lal

ANOMALOUS
INNERVATIONS
Chaman Lal Karotia (CK)
B.S.PT(KU); MPPS(Pak);
PG (Clinical NeurophysiolgyTechnology),(AKUH);
Member of AANEM; Member of ASET;
Aga Khan University Hospital , Karachi.

What is anomaly?
a·nom·a·ly (-nm-l) n:Gk, anomalos, irregular

A deviation from what is regarded as normal
or norm
Or
Marked deviation from normal, especially as
a result of congenital or hereditary defects.
anomalous, adj

15-X-12 Anomalous Innervations By:CK 3

Why is Important to know?

If these conditions remain unrecognized,
they can be mistakenly interpreted as
pathological conditions or technical faults.


A-Upper limb anomalous innervations

Martin – Gruber Anastomosis
(Median to Ulnar anastomosis)
All Ulnar- hand innervations
Ulnar to median anastomosis
Superficial Radial nerve innervations on
dorsum of the hand


B-Lower limb anomalous innervations

Accessory Peroneal nerve
Tibial to Peroneal anastomosis


Martin- Gruber anastomosis
It is most common anomalous innervation in
upper limb.
Present in 15 – 30 % of patients.
It is manifested by cross over of median-to-
ulnar fibres.
Cross over commonly occurs in mid forearm
either from the main median trunk or from
one of its branches (most commonly anterior
interossius nerve).
It may present unilaterally or bilaterally.
It involves only motor fibres.

Pathway and Innervation!
After cross over in the mid forearm, median
fibres run with the distal ulnar nerve to
innervate via any of the following means:
1. Innervation to hypothenar muscles(abductor
digiti minimi).
2. Innervation to FDI muscle.
3. Innervation to the ulnar innervated thenar
muscles.
4. Combination of these.

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Anomalous Innervations By:CK

When is it recognized ?

During routine ulnar conduction studies.
During ulnar conduction studies when
recorded from FDI.
During routine median studies.
When co- existent CTS study is
performed.


Recording During Routine Ulnar Studies

If anastomotic fibres innervate abductor digiti
minimi, > 10 % drop in CMAP amplitude is
noted between wrist and below elbow
stimulation sites.( Higher amplitudes are seen
with distal stimulation).
Median nerve stimulation should be performed
at the wrist and at the antecubital fossa (AF)
while recording the hypothenar muscles.


NCS recording from ADQ muscle


Cont’d…
The differential diagnosis of this pattern (i.e.,
higher amplitude distally than proximally) includes
the following:
1) Excessive stimulation of the ulnar nerve at the
wrist resulting in co-stimulation of the median
nerve,
2) Submaximal stimulation of the ulnar nerve at the
below-elbow site,
3) Conduction block of the ulnar nerve between the
wrist and below-elbow sites, or
4) An MGA with crossing fibers innervating the
hypothenar muscles.

Cont’d…
If no MGA is present, a small positive
deflection usually is recorded with both the
wrist and antecubital fossa stimulation sites,
reflecting a volume conducted potential from
median muscles.
If an MGA is present, a small positive
volume-conducted potential will be present
with median nerve stimulation at the wrist;
however, median stimulation at the
antecubital fossa will evoke a small CMAP
over the abductor digiti minimi.

Cont’d…

The amplitude of the CMAP evoked by
stimulating the median nerve at the ante-
cubital fossa (recording the hypothenar
muscles) will approximately equal the
difference between the CMAP amplitudes
evoked with ulnar nerve stimulation at the
wrist and below-elbow sites (recording the
hypothenar muscles).
If its not identified it may give a false
impression of technical fault or conduction
block.

NCS recoding from ADQ


Cross over of median to ulnar fibres supplying FDI

If anastomotic fibres innervate FDI, >10 % of
amplitude drop occurs between stimulation at
the wrist and below-elbow site. Higher
amplitude being found by distal stimulation.
It may give a false impression of technical
mistake or conduction block.

Question:- When NCS from FDI is done?


How to confirm for MGA ?
After ruling out the technical faults, median
nerve is stimulated at wrist and at anticubital
fossa while recording from FDI.
Higher amplitude CMAP is recorded with
proximal stimulation than with wrist
stimulation in case of MGA.
The difference between wrist and anticubital
fossa stimulations approximates the drop in
amplitude between proximal and distal
stimulation sites when stimulating ulnar
nerve.

NCS recording from FDI muscle


Cross over of median-to-ulnar fibres innervating
any of the ulnar innervated thenar muscles.

Adductor pollicis and deep head of flexor pollicis
brevis are ulnar nerve innervated thenar
muscles.
When these muscles are innervated by MGA,
median motor studies show a characteristic
pattern of higher CMAP amplitudes with
proximal median stimulation than distal
stimulation.


NCS recording from APB muscle


How to confirm for MGA ?
After ruling out the technical faults, ulnar nerve is
stimulated at the wrist and below elbow sites
while recording from thenar muscles.
Normally it results in a CMAP (due to ulnar
innervated muscles in thenar eminence) of
almost same amplitude, with proximal as well as
distal stimulation.
If an MGA is present, CMAP amplitude is lower
with proximal stimulation.


MGA with co existent CTS
As both of these conditions are common, so they
might be seen existing together.
Co existence of both the conditions should be
suspected when proximal median nerve
stimulation gives a more positive deflection at
the thenar eminence along with fast conduction
velocity.
In some cases of severe CTS, proximal latency
may be shorter than the distal latency.


15-X-12 26
Anomalous Innervations By:CK

Needle EMG in case of MGS
In this situation, unexpected results may be seen
creating confusion in interpretation. For
example,
In cases of median nerve dysfunction at the
anticubital site, EMG may show abnormal
findings in ulnar innervated muscles.
In cases of ulnar neuropathy, some of the ulnar
innervated muscles may be spared on EMG
examination.


All Ulnar- hand innervations
Among them are cases of the all-ulnar
hand. In rare individuals, all or most of the
intrinsic hand musculature is innervated by
the ulnar nerve. In these individuals, an
ulnar nerve lesion at the elbow may cause
much more dysfunction in the hand than
one typically expects to see.


Anomalous innervation between Superficial
Radial and the Dorsal Ulnar Cutaneous
sensory nerves
In the upper extremity, an anomalous
innervation between the superficial radial and
the dorsal ulnar cutaneous sensory nerves has
been described. Normally, sensation to the
dorsum of the hand is mediated by both
nerves: the little and ring fingers and medial
hand by the dorsal ulnar cutaneous nerve, and
the remainder by the superficial radial nerve. In
rare individuals, the superficial radial nerve
innervates the entire territory.

NCS recording in Sup.Radial v/s DUC
During nerve conductions, this situation may
present as an apparently absent response
recording the dorsal ulnar cutaneous sensory
nerve.
The anomaly can be demonstrated by
stimulating the superficial radial nerve in the
lateral forearm, with recording electrodes
placed over the dorsal ulnar cutaneous nerve
territory.


Accessory Peroneal Nerve (APN)
The most common anomalous innervation in
the lower extremity is the accessory
peroneal nerve (APN) in the lateral calf.
Patients with an APN have an anomalous
innervation to the EDB; the medial portion of
the EDB is supplied by the deep peroneal
nerve as usual, but the lateral portion is
supplied by an anomalous motor branch
originating from the superficial peroneal
nerve, the APN.

Tibial to Peroneal anastomosis
In addition, there are rare isolated case
reports of tibial-to-peroneal and ulnar-to-
median anastomosis. If an unusual or
unexpected nerve conduction pattern is
seen, one should always consider not only
technical factors but also the possibility of
an anomalous innervation.


Question:- All of the following can cause a
“positive dip” on routine NCS EXCEPT?

A. Co-stimulation.
B. Improper recording electrode placement.
C. MGA.
D. MGA with CTS.
E. Submaximal stimulation.


Answer:- C
Explanation:- When recording over the
thenar eminence and stimulating the
median nerve at the elbow, a positive dip
is not usually seen unless there is
concomitant CTS slowing down the action
potentials as they enter the hand.


Question:- In the MGA:
A. Some muscles in the thenar eminence
that are typically innervated by the median
nerve are innervated by the ulnar nerve.
B. The proximal median amplitude is always
higher than the distal median amplitude.
C. A pseudo-conduction block of the ulnar
nerve in the forearm may occur.


Cont’d. . .

D. The sensory potential recording from
digit two has contributions from the
median and ulnar nerves.
E. Individuals who have this variant may
have relative protection from median
neuropathy at the wrist.


Answer:- C
Explanation:- An MGA involving the ADQ
would be expected to produce a drop in
amplitude when comparing the distal site
with the proximal site. This will have an
appearance of conduction block in the
forearm and not across the elbow.


Anomalous innervations by;Chaman Lal

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