This document discusses anomalous innervations in the upper and lower limbs. It describes the Martin-Gruber anastomosis, which is the most common anomalous innervation in the upper limb, occurring in 15-30% of patients. It involves a crossover of median-to-ulnar fibers in the mid-forearm. The document also discusses the accessory peroneal nerve as a common anomalous innervation in the lower limb. Nerve conduction studies can help identify these anomalous innervations that could otherwise be mistaken for actual pathology.

1. Anomalous Innervations
Martin GruberAnastomosis, Accessory Peroneal
Anastomosis
DR BHAVIN J PATEL
SR NEUROLOGY
MBS HOSPITAL

2. Introduction
A deviation from what is regarded as normal
 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.

3. Types of Anomalous innervation
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

4. 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.

5. 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

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

7. 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 ante
cubital fossa (AF) while recording the hypothenar muscles (ADQ).

8. NCS recording from ADM muscle

9. Proximal MGA mimicking ulnar
neuropathy at elbow

10. NCS from APB in case of MGA
supplying thenar muscle.

11. 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.

12. 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,
4. An MGA with crossing fibers innervation the hypothenar muscles.

13. 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.

15. 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.

16. Anomalous innervation b/w superficial Radial
and Dorsal Ulnar Cutaneous sensory nerves
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.

17. Accessory deep peroneal nerve

18. Thank you

19. Sympathetic skin response (SSR)
• Thermoregulation is controlled by the sympathetic nervous
system, with the parasympathetic system playing a minor role
• Sympathetic sudomotor cholinergic fibers innervate sweat
glands to regulate evaporative heat loss

20. Indications of SSR
• Progressive autonomic failure syndromes
• Peripheral neuropathies where autonomic or other small fiber
involvement is suspected
• Distal small fiber neuropathies
• Diseases with sympathetically maintained pain

21. Protocol of SSR
• Low frequency (high pass) filter 0.1 or 0.5 Hz
• High-frequency (low pass) filter of 500 or 1000 Hz
• The gain 500 µV /Div
• The sweep 0.5-1 s/Div
• Temperatures are standardized to over 30°C, preferably over 32°C

22. Protocol of SSR
• The active electrodes are placed in the palm or sole and the reference
over the dorsum of the respective body part
• Electrodermal activity is brought out either directly or reflexly (electric
depolarization of a sensory nerve, startling auditory sound or deep
inspiratory gasps)
• Averaging should not be performed

23. Normal responses of SSR
• The morphology of the potentials are mono-, bi-, or triphasic
• Potentials are symmetric in homologous body regions.
• The potentials in the hands have larger amplitudes and shorter
latencies than those in the feet.
• Generally absent responses are considered to be abnormal

25. Normal Values of SSR
• The SSR is age dependent
– present in both hands and both feet in subjects under the age of 60
years
– only 50% of feet and 73% of hands in subjects older than 60years
• Mean latency in hands is 1.5 s, mean amplitude in hands is 0.450
mV, mean latency in feet is 1.9 s, and mean amplitude in feet is 0.15
mV

26. Advantages of SSR
• Sensitive, reproducible, semiquantitative, simple, fast, and readily
obtained on most electrophysiologic equipment
• SSR is comparable in its sensitivity to the quantitative sudomotor
axon reflex test (QSART) for the detection of autonomic dysfunction

27. Disadvantages of SSR
• Only semiquantitative
• May be difficult to elicit or be habituated and thereby be mistaken as
abnormal