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Bilateral involvement of the lateral cutaneous nerve of the calf in a diabetic.

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Bilateral Involvement
of the Lateral Cutaneous
Nerve of the Calf
in a Diabetic
Pasquale F. Finelli, MD,
and Margarete DiBenedetto, MD
The femoral, common peroneal (CPN), sciatic, ulnar, and
median nerves are among the most commonly involved
peripheral nerves in diabetes [ 3 ] . Common peroneal neuropathy may be bilateral as well as being a presenting manifestation of this disease [l]. We emphasize here that diabetics also may have increased vulnerability to pressure
neuropathy of the lateral cutaneous nerve of the calf
(LCNC).
For a year and a half, a 54-year-old man had noticed
From the Neurology Service, Veterans Administration Hospital,
and the Subsection of Neurology, Brown University Division of
Biological and Medical Sciences, Providence, RI, and the Rehabilitation Medicine Service, Veterans Administration Hospital,
West Roxbury, and Harvard Medical School, Boston, MA.
Accepted for publication Apr 24, 1978.
Address reprint requests to Dr Finelli, Veterans Administration
Hospital, Davis Park, Providence, RI 02908.
480 Annals of Neurology
decreased feeling on the lateral aspect of both legs from the
knee to approximately two-thirds of the way down the legs.
He denied other symptoms. The patient had been diabetic
for two years and had been treated with insulin, 30 units
N P H daily for eight months. He had suffered myocardial
infarctions in 1970 and 1972. After the second attack, he
spent most of the day sitting watching television with one
leg folded under his buttock and the other flexed at the
knee and resting on the opposite foot (Fig lA), periodically
alternating the leg flexed under the buttock. The abnormal
findings on examination were limited to absent deep tendon reflexes at the ankles and a sensory loss to light touch
and pinprick over the lateral aspect of both legs in the
distribution of the LCNC (Fig 1B).
Electromyography of the right peroneus longus muscle
showed silence at rest; on volition, an increase in mean
potential duration to 22 msec was observed. Polyphasia was
45%; amplitude was up to 2,000 pv; on maximal effort,
recruitment was slightly reduced (90 to 95%). EMG study
of the right gastrocnemius muscle showed silence at rest;
on volition, action potential amplitudes up to 2,500 pv
were observed with a mean potential duration of 10 to 12
msec and 30% polyphasia. O n maximal effort a full pattern
was recruited.
Pig 1. (A)Thepatient’s sittingposture. (8)Area of loss of light
touch sensation, with hatch marks showing area of decreaJed
pinprick sensation.
Vol 4 No 5 November 1978
common peroneal
nerie
nerve
I
.
l a t e r a l cutanews
nerve of calf
---
cutaneous
d i r t ributlon
it is unlikcly a compressive lesion of the C P N would selectively involve fibers of the LCNC without other clinical
evidence of peroneal nerve dysfunction.
Despitc electrophysiological evidence of a more diffuse
neuropathy, our patient’s symptoms were limited to the
LCNC. Recognition of rhis seemingly benign sensory
mononeuropathy may help avert a more disabling condition involving the CPN.
Rejerences
Shahani B, Spalding JMK:Diabercs mellirus presenting with
bilateral foor-drop. Lance: 2930-93 I. 1960
2. Sunderland S: Sciatic., rihial and common peroncal nerve lesions, in Nerves and Nerve Injuries. Baltimore, Williams &
Wilkins, 1963
3. Thomas PK, Eliason SG: Diahetic neuropathy. in Dyck PJ.
Thomas PK, Lamberr EH (eds): Peripheral Neuroparhy.
Philadelphia, Saunders. 1975, vol 2, pp 950 -981
1.
Fig 2. Lateral cntaneous newe ofthe calf with associated cntaiieouj dislribution.
Sensory nerve conduction of the superficial peronedl
nerve could not be visualized. The sural nerve showed a
latency of 3.4 msec at a distance of 13 cm from the
stimulating t o thc recording electrode (normal, 2.3 2 4)
with amplitucle of 10 p v (normal, 2 3 2 3) and duration of
1.4 msec (normal, 1.2 -C 0 I). Motor nerve conduction
studies of the right peroneal nerve showed a conduction
velocity of 34 m/sec below the knee to the ankle (normal,
45 5 5 ) and 28 mlsec from the popliteal fossa to below the
knee. The left peroneal nerve showed a conduction velocity of 38 d s e c below the knee to the ankle and 30 d s e c
from the poplireal fossa to below the knee.
The patient was instructed not to fold or cross his legs in
any way, and during a 10-day period regained approximately 90% of sensation over the involved area.
Discussion
The susceptibility of the CPN to compressive-ischemic
mechanisms with various postures of the lower extremity
has been described [2J, as has rapid improvement with
avoidance of the precipitating posture and extension of the
leg.
Between its origin in the popliteal fossa and its course
behind the head of the fibula, the C P N gives rise to a
cutaneous branch, the LCNC (Fig 2). Involvement of this
particular sensory branch is only occacionally an accompanying feature of a common pcroneal neuropathy, as the
site of injury of the C P N is usually at the fibular neck, a
point distal to the takeoff of the LCNC. T h e anatomical
pattern and superficial course of the LCNC may account
for selective damage of this nerve with sparing of the CPN.
Although partial injury of a major nerve can present as a
mononeuropathy in the distribution of one of its branches,
“Paradoxical Clonus”:
Rhythmic Contractions
Evoked in Passively
Shortened Muscle
Peter LeWitt. M D
Over a century ago, Wesrphal observed that shorteniilg as
well as strerching skeletal muscle can elicit contraction.
When passively slackened, muscle normally undergoes a
tonic contraction, termecl the shortening reaction (SR) by
some authors [ 5 I. T h e magnitude of contraction is affected
by disease of the motor system; the SR is abolished by
Jamage t o the corticospinal tract and is exaggcratcd in certain extrapyramidal disorders I I]. This report discusses
findings in a paucnt in whom the SR resembled clonus and
produced a marked contraction despite the absence of evident motor system ilisease.
A 71-year-old man was evaluated for an acute visual
cortex infarct. The patient was healthy and relaxcJ, and his
history and examination gave no evidence of neurological
abnormalities such as weakness, hyperreflcxia. tremor,
dystonia, parkinsonian features, o r clonus on muscle
stretch. When either ankle was dorsiflcxed passively, a
powerful contraction followed rapidly in the peroneal and
anterior tibial muscle groups, and this contraction evolveJ
into regular and sustained jerking. O n return of the ankle
to its neutral position, the jerking movements ceased.
There was no activation of the triceps surae <luring the
observed SR. T h e oscillation seen with the SR did not
From t h e Department of Neurology. Veterans Adminisrration
Hospital, Palo Alto, and Stanford University School o f Mcclicine.
Stanford. CA.
Accepted for publication May 2.3, 1078.
Address reprint rcquests to Dr LeWitt. Department of Neurology,
Veterans Administration Hospital, 380 1 Miranda Ave. Palo Alto.
CA 94304.
Notes and Letters 481
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