Case 26

Published on 03/03/2015 by admin

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Case 26

HISTORY AND PHYSICAL EXAMINATION

A 45-year-old man noted numbness in both toes for almost two years prior. The numbness had ascended to the ankles and lower legs. More recently, he noted numbness in the tips of his fingers. Burning pain followed in the same distribution. He also had mild imbalance. Upon review of systems, he admits to a 30 pounds weight loss over 3–4 years. He had mild hypertension and was on metoprolol. He smoked half a pack of cigarette a day and drank 1–2 pints of whiskey a day. There was no history of other toxic exposures or megavitamin consumption. There was no family history of neurological disease.

On examination, he was 6 ft 1 in tall and weighed 140 pounds. His lying and standing blood pressures were 140/85 and 138/80, respectively. His general physical examination was normal except for slight discoloration of skin in both feet with brittle toenails. Peripheral pulses were normal. On neurological examination, the mental status and cranial nerves were normal. The motor examination reveals atrophy of intrinsic muscles of foot bilaterally with mild weakness of ankle dorsiflexors and plantar flexors as well as toe extensors and flexors. There was no weakness or atrophy of hand muscles or proximal muscles. Sensory examination revealed a symmetrical decrease in pain, touch, and temperature sensations in both legs and fingers in a distal to proximal gradient. Position and vibration sense were diminished at the toes but normal elsewhere. Deep tendon reflexes were +2 and symmetrical in the upper extremities and at the knees while the ankle jerks were absent. Plantar responses were normal. Gait was normal but tandem gait was slightly impaired. Romberg test was negative. Electrodiagnostic (EDX) study was requested.

Please now review the Nerve Conduction Studies and Needle EMG tables.

QUESTIONS

1. All the following represent axonal polyneuropathies except:

A. Diabetic polyneuropathy.
B. Charcot-Marie-Tooth disease type 1.
C. Alcoholic polyneuropathy.
D. Critical illness polyneuropathy.
E. Charcot-Marie-Tooth disease type 2.

2. Electrodiagnostic features of axonal polyneuropathies include all the following except:

A. Conduction velocities greater than 80% of lower limits of normal.
B. Low compound muscle action potential (CMAP) amplitudes.
C. Low or absent sensory nerve action (SNAP) potentials.
D. Distal latencies greater than 120% of upper limits of normal.

3. Characteristics of alcoholic polyneuropathy include all the following except:

A. It is a chronic symmetric sensorimotor peripheral polyneuropathy.
B. It is easily distinguished from diabetic and uremic polyneuropathy.
C. It is often nutritional in origin.
D. It may respond to abstinence and vitamin supplementation.

EDX FINDINGS AND INTERPRETATION OF DATA

The abnormal EDX findings in this case include:

1. Absent sensory nerve action potentials (SNAP) in both lower extremities and low SNAP amplitudes in the upper extremities. This is symmetrical and worse in the lower than the upper extremities.

Case 26: Nerve Conduction Studies

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Case 26: Needle EMG

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2. Low compound muscle action potential (CMAP) amplitudes with either normal or borderline distal latencies, conduction velocities and F wave minimal latencies. This is symmetrical in the lower extremities and worse in the lower than the upper extremities. Also, it is worse distally in the lower extremities by comparing the peroneal motor conduction study recording extensor digitorum brevis to the study recording tibialis anterior.
3. Fibrillation potentials and decrease in motor unit action potential (MUAP) recruitment in the lower and upper extremities, worse in the lower and distally. The recruited MUAPs in the affected muscles are long in duration and, sometimes, high in amplitude and polyphasic.

The above findings are consistent with a generalized disorder affecting the sensory and motor fibers, worse distally. The recorded SNAPs and CMAPs are characterized by being low in amplitudes, but with either no or minimal slowing of distal latencies, conduction velocities, and F wave minimal latencies. These findings are diagnostic of a generalized, axonal, dying-back, sensorimotor, peripheral polyneuropathy, chronic with active (ongoing) denervation and reinnervation. This polyneuropathy is compatible with a wide range of disorders including alcoholic polyneuropathy, diabetic polyneuropathy, uremic polyneuropathy, nutritional polyneuropathy, or toxic polyneuropathy.

DISCUSSION

Definition and Pathogenesis

Peripheral Polyneuropathy

Peripheral neuropathy is a relatively common disorder with a prevalence that may reach up to 10% of the general population. Peripheral neuropathy is often a manifestation of a systemic disease such as diabetes, alcohol abuse, or leprosy. However, about 20% of neuropathies remain idiopathic; a significant number of these cases are likely inherited in nature.

The myriad of etiologies of peripheral neuropathy pose a daunting task for the clinician. Investigating peripheral neuropathy has included several approaches. First, is the pattern recognition approach where a diagnosis of a polyneuropathy is based on highly specific associated findings such as the Mee line in arsenic or thallium poisoning, red tongue in vitamin B12 deficiency, or predilection of the sensory loss to cool areas of the body (such as earlobes, nipples, and buttock) in leprosy. Unfortunately, this approach applies to a minority of patients usually with advanced disease, requires a vast clinical experience and is mostly accomplished by senior neurologists. The second approach frequently used by many physicians (including some neurologists) is a “shotgun” approach by ordering a battery of tests on every patient with a neuropathy. This irrational approach is costly and may result in incorrect diagnosis secondary to incidental abnormalities, such as elevated blood glucose in a patient with CIDP. The third recommended approach is a systematic approach that utilizes mainly the clinical findings and EDX studies to generate a more limited differential diagnosis and help guide the laboratory investigations necessary for establishing a final diagnosis (Table C26-1). Additional studies that are useful in the accurate diagnosis of peripheral neuropathy include autonomic testing, quantitative sensory testing, antibody testing, and skin or cutaneous nerve biopsy.

Table C26-1 Essential Steps in the Classification and Etiologic Diagnosis of Peripheral Polyneuropathy

The Temporal Profile of the Polyneuropathy
Is the polyneuropathy subacute or chronic?
If chronic, is the disorder progressive, relapsing and remitting, or stepwise?

Subacute – consider Guillain-Barré syndrome, porphyria, diphtheria, critical illness, and drugs/toxins
Chronic relapsing and remitting – consider CIDP and drugs/toxins
Chromic progressive – consider CIDP, metabolic disorder*, nutritional deficiency, and toxins
The Anatomic Pattern of the Polyneuropathy
Is the polyneuropathy distal, proximal, or both?
Are there any foot or spine deformities (pes cavus or kyphoscoliosis)?
Is the polyneuropathy symmetric or asymmetric?
If asymmetric, do the findings follow specific peripheral nerve distribution?

Distal – consider metabolic disturbance*, vitamin deficiency, toxins, drugs, critical illness, hereditary
Distal and proximal – consider Guillain-Barré syndrome, CIDP, porphyria
Asymmetric – consider vasculitis, CIDP, HNPP
Mononeuropathy multiplex – consider multifocal motor neuropathy, Lewis-Sumner syndrome, HNPP, vasculitis, leprosy
Pes cavus or kyphoscoliosis – consider CMT, HNPP

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