INTRODUCTION

 

In Egypt, 22% of the population is seropositive for HCV. In addition to the liver manifestations, chronic HCV infection may be associated with a series of extra hepatic manifestations including neuropathies. However, its pathogenesis is not completely understood. Peripheral neuropathy and detectable serum cryoglobulins appear in approximately one third of patients with HCV infection, but HCV-infected patients with peripheral neuropathy in the absence of serum cryoglobulins have also been described^1,2.

Cardiovascular autonomic neuropathy represents a serious complication of chronic liver cirrhosis. Autonomic neuropathy may also be regarded as a potential etiologic factor of hyperdynamic circulation and portal hypertension^3,4.

Evaluation of autonomic nervous system indicates both the sympathetic component and the parasympathetic division. Both the sympathetic skin response {(SSR) and the heart rate variability} may be simple means of assessing autonomic function^5,6.

The SSR which is a polysynaptic reflex generated in the deep layers of the skin by activation of sweat glands via sudomotor sympathetic efferent fibers^7,8.

Heart rate variability is a useful, sensitive and non-invasive test used to assess the parasympathetic autonomic functions. It is defined as the variation in the length of the intervals measured in milliseconds (ms) between heart beats and it refers to beat-to-beat alterations in heart rate^9,10.

 

Aim of the work:

Due to the importance and prevalence of HCV in Egypt, this study was carried to delineate the spectrum of HCV associated sensory and autonomic neuropathy and assess its relation to liver affection.

 

PATIENTS AND METHODS

 

Patients:

This study was conducted on two groups, control and patients group.

a.    Control Group:

                   It included 20 volunteers of both sexes (8 males and 12 females). Their mean age 40.65±9.9 years. They were in perfect general health and causes of autonomic and peripheral neuropathy were excluded.

b.    Patients Group:

Patients group included 40 patients with HCV infection; 21 males and 19 females were selected from Internal Medicine Department, Cairo University Hospitals. They were divided into two sub groups by abdominal ultrasound and laboratory investigations:

1.   Chronic active hepatitis group. 20 patients suffering from chronic active hepatitis without cirrhosis with a mean age of 42.1±10.00.

2.   Cirrhotic group. 20 Patients suffering from cirrhosis with a mean age of 45.95±9.7.

 

Methods

Patients group was subjected to careful history taking especially for autonomic and peripheral symptoms and signs:

A)            Autonomic symptoms and signs:

1.   Orthostatic hypotension, vertigo, dizziness and syncope.

2.   Sweating on a hot day, during fever or after a hot shower.

3.   Impotence.

4.   Dry eyes and dry mouth.

Careful clinical examination especially for autonomic dysfunction in the form of:

1-      Blood pressure measurement at recumbent and on standing upright. A drop in systolic pressure > 20 mmHg or drop of diastolic blood pressure > 10 mmHg is pathognomonic.

2-      Trophic changes: signs of thickening, discoloration or excessive fragility of nails and alopecia.

 

B)            Peripheral symptoms and signs:

1.   Fatigue and weakness.

2.   Loss of balance particularly in the dark.

3.   Dizziness, especially when getting up from abed or a chair.

4.   Numbness, especially of hands or feet.

5.   Pain, often burning or shooting in quality.

6.   Muscle wasting in the hands and feet.

7.   Loss of reflexes.

 

All the candidates of the study were subjected to the following investigations:

1.             Fasting and post prandial blood sugar. 

2.             Thyroid function tests: T₃, T₄ and TSH.

3.             HCV antibody and PCR

4.      Renal function tests: Blood urea and serum creatinine.

5.             Complete blood count (CBC)

6.             Liver function tests:

 

Alanine amino tranferase, serum albumin, serum bilirubin, prothrombin time (PT) and prothrombin concentration (PC).

1-         Abdominal ultrasound.

2-         Electro physiological study for sensory nerves and SSR test using Nihon kohden 2 channels EMG and evoked potential system.  For the RRV machine used was DANTEC, key point, software version 1.6.

 

I. Sensory nerve assessment

 

a)             Ulnar Nerve stimulation

Pickup: Ring active and reference electrodes are placed on the fifth digit with at least a 4-cm separation, if possible. The active is proximal at the base of the digit.

Ground: The ground is between the stimulating and pickup electrodes.

Stimulation: Stimulation is applied 14cm proximally to the active recording electrode, just radial to the flexor carpiulnaris. The cathode is distal i.e.: antidromic. Stimulation is applied proximally at the elbow in the ulnar groove. 

Machine settings:

·                     Frequency: 8 Hz to 1.6 kHz.

·                     Sweep speed: 2 msec/div

·                     Gain: 10 μV.

 

b)             Medial Plantar Nerve stimulation

Pickup:  The active surface electrode is on the big toe.

Reference: 3 cm distal to active one.

Ground: The ground is on the dorsum of the foot.

Stimulation: Distal distance is measured from the pickup of the medial planter nerve following the course of the nerve 1cm posterior to the medial malleolus, with the stimulation occurring posterior to the medial malleolus and above the flexor retinaculum.

Machine Settings:

·                     Frequency: 8 Hz to 1.6 kHz

·                     Sweep speed: 5 msec/div.

·                     Gain: 20 μV.

 

II.    Autonomic nervous

system assessment

 

a)             Sympathetic skin response test (SSR):

SSR test was performed in a quiet semi- dark room of comfortable temperature (ranged from 22˚C to 24˚C) to all subjects. The subject lied semi setting and was asked to relax for 10-15 minutes prior to the test.

§             Stimulating and recording electrodes: A bipolar stimulator surface electrodes were used. It was applied to the wrist joint of the contralateral upper limb and to the plantar surface at the midfoot of the contralateral lower limb.

                The stimulator was usually positioned so that the cathode is directed proximally. The recording electrodes were in the form of surface disk electrodes applied with adhesive paste after thorough cleaning with alcohol.

 

They were applied as follows:

1.      In the upper limb: The active electrode was placed over the second palmar interspace 3 cm proximal to the web space, the reference electrode over the pulp of the middle finger.

2.      In the lower limb: The active electrode was placed over the second plantar interspace in the midfoot and the reference electrode at the pulp of the second toe.

 

                The recording was from the left side and the stimulation was 20 to 40 mA., with duration 0.2 msec., and rate of stimulation 0.1 sec. Low filter was 0.5 Hz, and high filter was 5 KHz, the interstimulus interval was 1 minute. The latency and amplitude were measured.

                After 5 minutes another response is elicited to ensure the consistency of the first one.

 

Parameters for evaluation

Latency and amplitude were measured so that the latency is the time between the stimulus artifact and the beginning of the response msec. in sensory nerves, and the amplitude is a peak to peak difference measurement in micro volt (μv)

As regard the SSR test the latency is measured in seconds (because of the slow conducting c fibers) and amplitude in milli volt (mv).

 

b)      Heart rate variability test (R-R interval test):

RR interval tests were performed-in a quite semi-dark room of comfortable temperature (ranged from 22˚C to 24˚C)-to all subjects. The subject lied in a semi- setting and was asked to relax for 10-15 minutes prior to the test.

Two surface disk stainless steel electrodes 1 cm in diameter were applied on each arm (we applied the electrode over the radial pulse as standardized site) with adhesive paste after thorough cleaning with alcohol. They were applied where active electrode on the right arm, reference electrode on the left and the ground usually applied on the right arm. The heart beat were measured and the time interval between heart beats were displayed.

 

Procedures were done as follows:

1.             Normal breathing

2.             6-10 cycles of Deep breathing

 

* R-R interval: the time to previous peak

 

The R-R interval variability was calculated as follows:

* RRV during normal breathing:

 

*RRV during 6-10 cycles of deep breathing

 

 

RESULTS

 

The 3 groups (Control group, patients group suffering from cirrhosis, patients group suffering from chronic active hepatitis) are age and sex matched.

The difference between cirrhosis patients and patients suffering from chronic active hepatitis regarding hypothesia was statistically significant (P<0.05), also there were differences between two groups regarding tingling, impotence, trophic changes and orthostatic hypotension, sweating, dizziness, vertigo with more affection of the cirrhotic group but it was not statistically significant (Table 1).

 

Sensory nerve conduction study:

The differences between the groups regarding the amplitude and conduction velocity of  the medial plantar nerve sensory response were highly statistically significant (P value = 0.001) (Figs. 1,2,3) also there were differences between the groups regarding the amplitude and latency of the ulnar nerve sensory response with more affection of the cirrhotic group but it was not statistically significant (Table 2).

 

SSR of the upper and lower limbs:

There was a high statistically significant reduction of the amplitude in the cirrhotic group (P value = 0.001), also the latencies were prolonged but it was not statistically significant (Tables 3, 4 and Fig. 4).

 

Heart rate variability (R-R interval):

As regards the H.R.V during normal breathing, there was a statistically significant difference between the control group and the cirrhotic group (P value = 0.03). However there was no significant difference between the control group and the chronic active hepatitis one nor the cirrhotic group and the chronic active hepatitis group (P value = 0.07, 1.0 respectively).

As regard the H.R.V during deep breathing, there was a statistically high significant difference between the control group and the cirrhotic group as well as between the control group and the chronic active hepatitis one (P value = 0.000). However there was no significant difference between the cirrhotic group and the chronic active hepatitis group (P value 1.0) (Table 5 and 6).

 

Relations between the clinical findings and the electrophysiological data (Table 7):

There was a statistically significant difference between those patients with clinical sensory abnormalities and those without regarding sensory  nerve conduction studies being more affected in the patients with clinical sensory abnormalities (P  value = 0.02). However there was no significant difference between those patients with autonomic dysfunction and those without regarding the neurophysiological autonomic tests (SSR, RRV) tests (P value = 0.6) (Fig. 5).

 

Percentage of abnormalities among different neurophysiological parameters (Table 8):

Sensory neuropathy was found in 12 patients (60%) with chronic active hepatitis and 18 patients (90%) with cirrhosis.

Sympathetic neuropathy was found in 15 patients (75%) with chronic active hepatitis and 18 patients (90%) with cirrhosis.

Parasympathetic neuropathy was found in 13 patients (65%) with chronic active hepatitis and 14 patients (70%) with cirrhosis.

Polyneuropathy sensory and/or autonomic were found in 15 patients (75%) with chronic active hepatitis and 18 patients (90%) with cirrhosis (Fig. 6).

 

Table 1. Clinical manifestations of peripheral and autonomic neuropathy in different groups.

 

Data	Cirrhotic (n = 20)		Chronic active hepatitis (n = 20)		P –value
	N.	%	N.	%
Hypothesia	9	45	2	10	<0.05*
Tingling	6	30	3	15	> 0.05
Impotence	1	5	0	0	> 0.05
Trophic changes	3	15	0	0	>0.05
Orthostatic hypotension	3	15	0	0	>0.05
Sweating	3	15	1	5	> 0.05
Dizziness	2	10	1	5	> 0.05
Vertigo	3	15	2	10	> 0.05

*significant

 

Table 2. Sensory nerve conduction study in the ulnar and medial plantar nerves in the different groups of the study.

 

Data	Cirrhotic (n = 20)	Chronic active hepatitis (n = 20)	Control  (n = 20)	F	P-value
	mean±SD	mean±SD	mean±SD
Ulnar. n. sensory latency (m sec)	3.48±2.12	3.18±1.38	2.72±0.13	1.34	0.27
Ulnar. n. sensory amplitude (μv)	8.25±5.5	10.55±3.09	10.66±1.1	1.91	0.07
Medial plantar n.sensory cv (m/sec)	25.89±12.27	34.42±4.51	34.76±2.32	8.58	0.001**
Medial plantar n. sensory amplitude (μv)	2.54±1.23	3.26±0.8	3.58±0.1	7.59	0.001**

**highly significant

 

Table 3. Sympathetic skin response (SSR) in the upper and lower limbs in the different groups of the study.

 

Data	Cirrhotic (n = 20)	Chronic active hepatitis (n = 20)	Control  (n = 20)	F	P-value
	mean±SD	mean±SD	mean±SD
SSR latency in UL (sec)	2.14±1.43	1.63±0.11	1.6±0.1	2.66	0.07
SSR amplitude in UL (m v)	1.36±0.5	1.72±0.15	1.7±0.23	7.5	0.001**
SSR latency in LL (sec)	3.03±1.7	2.68±0.14	2.68±0.15	0.85	0.43
SSR amplitude in LL (m v)	0.37±0.3	0.66±0.15	0.56±0.15	9.19	0.001**

**highly significant

Table 4. Difference between the 3 groups as regards the significant neurophysiological parameters.

 

Dependent variable	Groups	Groups	P-valve
Medial planter CV (m/Sec)	Cirrhotic	Chronic active hepatitis	0.003**
	Cirrhotic	Control	0.002**
	chronic active hepatitis	Control	1.000
Medial planter amplitude uv	Cirrhotic	Ch. active hepatitis	0.03*
	Cirrhotic	Control	0.001**
	chronic active hepatitis	Control	0.790
SSR upper limb amplitude mv	Cirrhotic	Ch. active hepatitis	0.003**
	Cirrhotic	Control	0.006**
	chronic active hepatitis	Control	1.000
SSR lower limb amplitude mv	Cirrhotic	Ch. active hepatitis	0.000**
	Cirrhotic	Control	0.024
	chronic active hepatitis	Control	0.431

**highly significant.                                * significant

 

Table 5. Heart rate variability results in patients and control.

 

Variable	Group	No.	Mean±SD
HRV-normal breathing	Ch. active	20	78.7±11.2
	Cirrhotic	20	86.5±10.3
	Control	20	77.6±10.2
HRV-deep breathing	Ch. Active	20	109.2±18.3
	Cirrhotic	20	116.5±22.0
	Control	20	70.4±41.3

 

Table 6. Difference between groups as regards Heart rate variability.

                                                         

Variable	Groups	Groups	P. valve
HRV-normal breathing	Control	Chronic active hepatitis	.07
	Control	Cirrhotic	.03*
	Chronic active hepatitis	Cirrhotic	1.0
HRV-deep breathing	Control	Chronic active hepatitis	0.000**
	Control	Cirrhotic	0.000**
	Chronic active hepatitis	Cirrhotic	1.0

**highly significant                                 * significant

 

Table 7. Relations between the clinical findings and the electrophysiological data.

                                       

Clinical symptoms	Sensory		Autonomic
	Negative (n=10)	Positive (n=30)	Negative (n=7)	Positive (n=33)
	N	N	N	N
Negative (n=31)	10	19	6	23
Positive  (n=9)	0	11	1	10
p-value	0.02*		0.67

* significant

Table 8. Percentage of abnormalities among different neurophysiological parameters.

 

Neurophysiological test	Ch. active hepatitis	Cirrhotic
Ulnar and/or medial plantar latency or cv and/or amplitude	12patients (60%)	18 patients (90%)
SSR UL and/or LL	15 patients (75%)	18 patients (90%)
Heart rate variability	13 patients (65%)	14 patients (70%)
Polyneuropathy sensory and/or autonomic	15 patients (75%)	18 patients (90%)

 

 

 

Fig. (1): Mean medial planter n. sensory CV (m/sec) in the three studied groups.

 

 

Fig. (2): Mean medial planter n. sensory amplitude (uv) in the three studied groups.

 

Fig. (3): Affected medial plantar response (reduced CV, small amplitude).

 

 

 Fig. (4): Small amplitude SSR in the lower limb.

 

 

 

Fig. (5): Difference between patients with clinical sensory abnormalities and those

without regarding sensory nerve conduction studies

Fig. (6): Polyneuropathy sensory and/or autonomic among cirrhotic and ch. active hepatitis patients.

 

DISCUSSION

 

Peripheral neuropathy is a common complication of HCV infection. However, few have investigated the prevalence of the peripheral neuropathy in HCV patients¹¹.

The pathophysiology of HCV related peripheral neuropathy remains largely speculative; vascular deposition of HCV RNA containing cryoglobulins, direct viral infection or perivascular mononuclear inflammatory cells may be at the origin of HCV associated peripheral neuropathy^12,13,14,15.

Cardiovascular autonomic and peripheral sensory neuropathy are complications of chronic liver cirrhosis, the cardiovascular autonomic neuropathy represents a serious complication as it carries a 5 –fold risk of mortality in patients with chronic liver disease^16,17. Also autonomic neuropathy should be taken into consideration for early liver transplantation in patients with advanced liver disease to avoid the high mortality rate after transplantation⁴. In this study, the clinical and electrophysiological spectrum of HCV associated polyneuropathy and autonomic neuropathy has been explored. 

Regarding the clinical neurological findings tingling, hypothesia, sweating, dizziness and vertigo were more prevalent in the cirrhotic group 30, 45, 15, 10, 15% than the chronic active group 15, 10, 5, 5, 10% respectively. Trophic changes, orthostatic hypotension, impotence were only found in the cirrhotic group with a percentage 15, 15, 5% respectively. Sensory and autonomic dysfunction were more prevalent in the cirrhotic group than the chronic active group agree with Chaudhry et al.¹⁸ and Bajaj et al.¹⁹, who reported that sensory and autonomic dysfunctions are more frequent in advanced liver affection.

As regards the electrophysiological findings there was a high statistically significant reduction in amplitude and conduction velocity of the medial plantar sensory response in the cirrhotic group as compared to the control one (P value = 0.001, 0.002) and as compared to the chronic active group (P value = 0.03, 0.003) respectively.

It is known that SSR test is a useful test used to assess the sympathetic dysfunction^5,6. In this study there was a high statistically significant reduction in the amplitude of the SSR test in the upper and the lower limbs in the cirrhotic group as compared to the chronic active group (P value = 0.003, 0.000) and the control one (P value =0.006, 0.02) respectively. However, there were no significant difference between the control and the chronic active hepatitis groups as regards any of the neurophysiological parameters. These results are in agreement with Chaudhry et al.¹⁸ and Kharbonda et al.²⁰, who found that the prevalence and severity of peripheral and autonomic neuropathy was related to the severity of hepatic dysfunction.

In our study the sensory peripheral neuropathy was significantly found in the patients group with cirrhosis in the lower limbs (P value = 0.001), the more prevalence of abnormalities in the lower limbs agree with Chaudry et al¹⁸. However, the autonomic neuropathy was significantly present in the lower limbs as well as the upper limb (P value = 0.001) also in the cirrhotic group only.

However the amplitude reduction was highly statistically significant in the cirrhotic group as compared the chronic active group regarding the SSR of the upper and lower limbs (P value = 0.003, 0.000) respectively and the medial plantar sensory response amplitude (P value = 0.03). These findings support the theory that peripheral neuropathy in HCV infection is axonal mostly due to nerve ischemia.  The reduced conduction velocity may be due to secondary demylination after axonal affection and are more frequent in advanced liver disease ^11,22. These agree with Riplaut et al.²¹. 

It is known that H.R.V is a useful, non-invasive test used to assess the parasympathetic dysfunction ^5,6. In this study, H.R.V during normal breathing showed a statistically significant variability among the cirrhotic group as compared to the control one (P value = 0.03). However the H.R.V during deep breathing, showed a statistically high significant variability among the cirrhotic group, chronic active hepatitis group as compared to the control one (P value = 0.000). However there was no significant difference between the cirrhotic group and the chronic active hepatitis group (P value = 1.0). These indicate there is sympathetic and parasympathetic dysautonomia in chronic active hepatitis as well as cirrhotic groups .

There was a statistically significant difference between those patients with clinical sensory abnormalities and those without regarding sensory  nerve conduction studies being more affected in the patients with clinical sensory abnormalities (P value = 0.02). However there was no significant difference between those patients with autonomic dysfunction and those without regarding the neurophysiological autonomic tests (SSR, RRV) tests (P value = 0.6) this may be due to the small number of the clinically affected patients as regard autonomic dysfunction . 

Clinical assessment revealed polyneuropathy in chronic active and cirrhotic groups 15% and 45% respectively. However, detailed electrophysio-logical assessment revealed polyneuropathy 75, 90 % respectively, our results are in agreement with those of Kharbanda et al.²⁰, who reported that nerve conduction studies were abnormal in 73% of patients with liver cirrhosis and fierro et al.²³, who reported clinical signs of peripheral neuropathy were found in 21% of patients while electrophysiological impairment were found in 57.8%. Our higher percentages are mostly due to the detailed assessment of the small fiber neuropathy carried out by the SSR test ,and the electrophysiological parasympathetic assessment that was lacking in the previous studies.

Therefore pure clinical assessment have relatively poor diagnostic accuracy in predicting the presence of polyneuropathy and tends to underestimate peripheral nervous system involvement in the HCV, as pointed out by England et al.²⁴ .

 

Conclusion:

Polyneuropathy is common in patients with hepatitis C. Electrophysiological examinations can detect degree and type of sensory and autonomic dysfunction. Also they give quantitative data about subclinical peripheral neuropathy.

 

REEFRENCES

 

1.      Lidove O, Cacoub P, Maisonobe T, et al. (2001): Hepatitis C virus infection with peripheral neuropathy is not always associated with cryoglobulinaemia, Ann Rheum Dis. 60: 290-2.

2.      Zaltron S, Puoti M, Liberini P et al. (1998): High prevalence of peripheral neuropathy in hepatitis C virus infected patients ,J. Gastroenterol. Hepatol. 30: 391-5.

3.      Kempler, Toth T, Szalay F (1996): May Autonomic neuropathy play a role in the development of hyperdinamci circulation and portal hypertension in chronic liver diseases? (Hypothesis). In: Aquino AV, Picdad FF, Sulit YQM (eds). 23^rd Congress of the international Society of internal Medicine Monduzzi Sditore Bologna Italy 251: 254.

4.      Fleckenstein JF, Frank S, Thuluvath PJ (1996): Presence of autonomic neuropathy is a poor prognostic indicator in patients with advanced liver disease, Hepatology 23: 471-475.

5.      Adams, R.D, Victor M, and Ropper A.H (2001): Disorders of the autonomic nervous system. In: Principles of Neurology, 7^th edition.1-

6.      Low PA, Vernino S, Suarez G (2003): Autonomic dysfunction in peripheral nerve disease, Muscle Nerve Jun;27 (6): 646-61.

7.      Shahani B, Halperin J, Boulu P, Cohen J (1984): Sympathetic skin response-a method of assessing unmyelinated axon dysfunction in peripheral neuropathies, J. Neurol. Neurosurg. Psychiatry, 47:536-542

8.      Claus D, Schondorf R (1999): Sympathetic skin responses. (The International Federation of Clinical Neurophysiology). Electroencephalogr. Clin. Neurophysiol., Suppl. 52: 277-282.

9.      Persson A, Solders G (1983): R-R variations, a test of autonomic dysfunction, Acta. Neurol. Scand., 67:285-293.

10.    Malik K.M. ,Camm J. (1995): Heart rate variability. Armonk NW: Future Publishing.

11.    Nemni R, Sanvito L, Quattrini A (2003): Peripheral neuropathy in hepatitis C virus infection with and without cryoglobulinaemia, J Neurol Neurosurg Psychiatry 74: 1267-71.

12.    Agnello V, Chung RT, Kaplan LM (1992): A role for hepatitis C virus infection in type II cryoglobulinemia, N Engl J Med; 327: 1490.

13.    Agnello V, Abel G (1997): Localization of hepatitis C virus in cutaneous vasculitic lesions in patients with type II cryoglobulinemia. Arthritis Rheum; 40: 2007–15.

14.    Bonetti B, Invernizzi F, Rizzuto N (1997): T-cell-mediated epineurial vasculitis and humoral-mediated microangiopathy in cryoglobulinemic neuropathy. J neuroimmunol 73: 145-54.

15.    Bonetti B, Scardoni M, Monaco S (1999): Hepatitis C virus infection of peripheral nerves in type II cryoglobulinaemia. Virchows Arch 434:533-5.

16.    Hendrickse MT, Thuluvath PJ, Triger DR (1992): The natural history of autonomic neuropathy in chronic liver disease, Lancet 339: 1462-1464.

17.    Szalay F, Marton A, Kereztes K, Hermanyi ZS, Kempler P (1998): Neuropathy as an extrahepatic manifestation of chronic liver diseases. Scand J. Gastroenterol 228 (suppl): 130-132

18.    Chaudhry, V, Corse A. M, O`Brian R (1999):  Autonomic and peripheral (sensorimotor) neuropathy in chronic liver disease: A clinical and electrophysiological study. Hepatol. 29: 1698-1703

19.    Bajaj BK, Agarwal MP, Krishna BR (2003): Autonomic neuropathy in patients with hepatic cirrhosis. Postgraduate Medical Journal. 79: 408-411.

20.    Kharbanda PS, Prabhakar S, Chawla YK, Das CP, Syal P (2003): Peripheral neuropathy in liver cirrhosis. J Gastroenterol Hepatol. Aug; 18 (8): 922-926.

21.    Ripault MP, Borderie C, Dumas P, (1998): Peripheral neuropathies and chronic hepatitis C: a frequent assoication? Gastroenterol clin Biol 22: 891-6.

22.    Santoro L, Manganelli F, Briani C, Giannini F, Benedetti, Vitelli E, Mazzeo A, Beghi E (2006): prevalence and characteristics of peripheral neuropathy in hepatitis C virus population Jounal of Neurology, Neurosurgery, and Psychiatry 77: 626-629

23.    Fierro B, Raimondo D, Castiglione MG, Migneco G, Scoppa F, Savettieri G (1986): Ital J Neurol Sci Dec; 7 (6): 586-90.

24.    England JD, Gronseth GS, Franklin G (2005): Distal symmetrical polyneuropathy: definition for clinical research. Muscle Nerve 31: 113-23.