Anomalous Innervation. These are the sort of normal variants which can be found in any normal subject or can concomitantly be found or superimposed in pathological cases. Identifying these anomalies helps out interpreting and making correct diagnosis and to avoid any misinterpretation.

1. Anomalous Innervations
• Presented by
Syed Irshad Murtaza
• Neurophysiology Department
• Dr. Ziauddin University Hospital,
• Clifton Campus, Karachi.
• 20-10-2015
Martin Gruber Anastomosis, Accessory Peroneal Anastomosis.

2. Anomalous Innervations
• 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

3. Why is Important to know?
• If these conditions (anomalies) are not
recognized, they may easily be mistaken for
technical fault & abnormalities or, in some
cases, for actual pathology which would not
be existing in actual.

4. TYPES of Anomalies
• 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

5. Martin- Gruber anastomosis (MGA)
• 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
• fibers.
• Cross over commonly occurs in mid forearm
• either from the main trunk of median nerve or from
• one of its branches (most commonly anterior
• interosseus nerve).
• It may present unilaterally or bilaterally.
• It involves only motor fibers while sensory are spared.

6. ANATOMY
• Pathway and Innervation!
• After cross over in the mid forearm, median fibers run with
the distal ulnar nerve to innervate any of the following ulnar
muscles:
• 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.

7. When & how MGA is Recognized ?
• 1. During routine ulnar conduction studies.
• 2. During ulnar conduction studies when recorded
from FDI.
• 3. During routine median studies recording from
APB.
• 4. When co- existent CTS study is performed.

8. Routine Ulnar Conduction Study
• If anastomotic fibers innervate abductor digiti
• Minimi (ADM) > 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 (ADQ).

9. Anastomosis (Crossing over of Fibers

10. NCS recording from ADQ muscle

14. Marinacci communication (ulnar-to-median
anastomosis in the forearm)
• Prevalence of MGA, an anomalous median-to-ulnar forearm
communication, is well reported in literature while Marinacci
communication, the reverse of Martin-
• Gruber with forearm ulnar-to-median communication is
underrecognized . Marinacci (in 1964) first reported patient who,
following trauma to the median nerve at the forearm, had
preservation of median nerve innervated
• hand muscles despite denervation of forearm flexors.
• Marinacci communication involving only sensory nerve fibers rise
from the median nerve distally to ulnar nerve proximally has been
reported. In the patient, reported by Hopf , that the nerve action
potentials evoked by
• stimulation of the middle finger (ulnar side) and the ring finger
(radial side) digital nerves were propagated with the median nerve
at the wrist and the ulnar nerve at the elbow.

15. Differential Diagnosis of MGA
• 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 innervation the
hypothenar muscles.

16. 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 wrist, however,
median stimulation at the antecubital fossa
will evoke a small CMAM over the abductor
digiti minimi.

17. 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.

18. NCS Recording from ADQ

19. Recording from ADQ muscle

20. Cross Over of Median to Ulnar Fibers Supplying FDI
• If anastomotic fibers 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.
• Q. When NCS is needed to perform from FDI?

21. How to Confirm MGA?
• After ruling out the technical faults, median nerve
is stimulated at wrist and at ante-cubital 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 antecubital
fossa stimulations approximates the drop in
amplitude between proximal and distal
stimulation sites when stimulating ulnar nerves.

22. Riche-Cannieu anastomosis
• Riche-Cannieu anastomosis (ulnar-to-median
anastomosis in the hand)
• In the hand, Riche (1897) and Cannieu (1897)
described a neural connection between the
deep branch of the ulnar nerve and the
recurrent branch of the median nerve at the
• thenar eminence

23. Cross over of median and ulnar fibers

24. NCS recording from FDI muscle.

25. • Cross over of median-to-ulnar fibers innervating
any of the ulnar innervated thenar muscles.
• Abductor 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.

26. NCS Recording from APB muscle.

27. How to confirm 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.

28. MGA

29. How to Confirm 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.

30. 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.

31. MGA with co existent CTS

32. Needle EMG in case of MGA
• In this situation, unexpected results may be
seen creating confusion in interpretation.
For example
• In cases of median nerve dysfunction at the
antecubital 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.

33. All Ulnar Hand Innervation
• Among the anomalies are cases of the all-
ulnar hand innervation. 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.
•

34. Anomalous innervation b/w superficial Radial
and Dorsal Ulnar Cutaneous sensory nerves
• In the upper extremity, an anomalous
innervation b/w 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 nerves,
and the remainder by the superficial radial
nerve. In rare individuals, the superficial radial
nerve innervated the entire territory.

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

36. Radial to DUC crossing

37. Accessory deep peroneal nerve
• The deep peroneal nerve, a major branch of the common
peroneal nerve, usually innervates the EDB. In 21-28% of
subjects, this muscle also receives innervation from the
accessory deep peroneal nerve, an anomalous branch of the
superficial peroneal nerve.
• This anomaly should be suspected when proximal stimulation
of the common peroneal nerve at the knee elicits higher
amplitude CMAP, than stimulation of the deep peroneal nerve
at the ankle. Stimulation of the accessory deep peroneal nerve
behind the lateral malleolus activates the anomalously
innervated lateral portion of the EDB.
• Rarely, this anomalous branch may exclusively supply the EDB.
In the presence of this anomaly, the lesions of the deep
peroneal nerve spare the lateral portion or the whole of the
EDB, thus leading to the possibility of an incorrect conclusion.

40. Accessory Peroneal
Peroneal motor NCS
Recording Site : EDB
STIMULUS SITE LAT1 DUR AMP AREA
ms ms mV mVms
A1: Ankle 5.2 10.6 1.260 3.392
A2: Below Fib. head 11.8 10.7 2.641 8.191
A3: Above Fib. head 15.1 11.7 2.428 8.610
A4: Behind lat. mall 4.9 11.1 1.578 5.331
SEGMENT DIST DIFF CV
ms ms m / s
Ankle-Below Fib. head 325 6.6 49
Below Fib. h-Above Fib. h 225 3.3 68

41. 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.

44. ,.

45. References
• Electromyography and Neuromuscular Disorders
by David C Preston MD
• Clinical Electromyography: Nerve Conduction
Studies &
• Principles of Clinical Electromyography
by Shin J. Oh, MD
• Electrodiagnosis in Diseases of Nerve and Muscle
by Jun Kimura MD
AKUH Karachi and Dr.Ziauddin University Hospital, Clifton
Campus Karachi, Neurophysiology Department Specific
Techniques, Protocols and Methods of Performing NCS/EMG
with Normative Data.