A case of Tropical ataxic neuropathy

Case Report

A case of Tropical ataxic neuropathy

V.L. Arul Selvan

Consultant Neurologist, Apollo Institute of Neurosciences, Chennai, India

a r t i c l e i n f o

Article history:

Received 23 July 2013

Accepted 7 August 2013

Available online 31 August 2013

Keywords:

Tropical ataxic neuropathy

Cyanide

Tanzania

a b s t r a c t

Tropical ataxic neuropathy is endemic to certain parts of the world and is causally related

to the regular long term intake of cassava. The Cyanogen, Linimarin and its subsequent

metabolism leading to the release of cynanide and thiocyanate and the development of

deficiency of sulphur containing amino acids lead to the neurotoxicity which presents as

predominant sensory neuropathy with ataxia. We report a young patient from Tanzania

with the disease and highlight the importance of dietary history in patients with unex-

plained neurological illness.

Copyright ª 2013, Indraprastha Medical Corporation Ltd. All rights reserved.

1. Case report

A 19 year old gentleman from Tanzania came to Apollo Hos-

pitals, Chennai with a history of progressive unsteadiness of

walking of 3 years duration which was insidious in onset. He

gave history of numbness of feetwhich spread gradually to his

legs and to his right thigh of 2 1/2 years duration. He felt more

unsteady in the dark and during the day, he was mostly in-

doors as he needed support to walk on the road. He had

burning sensation and paresthesis initially, which have

reduced subsequently. He also had increased sweating all over

his upper body. He did not have any weakness but had slip-

ping of his chappals without his awareness. He had no thin-

ning of muscles or twitching but had occasional calf cramps.

He had no symptoms referable to the higher Cognitive func-

tions, Cranial nerves, Upper limbs, neck or trunk. He had no

bowel or bladder related symptoms or orthostatic giddiness.

He had hypopigmented, macular skin lesions over the neck,

upper limbs and trunk but no nail or mucosal symptoms.

Therewere no constitutional symptoms. Therewas no history

of similar symptoms in the family or immediate

neighbourhood.

On examination, he had extensive Taenia versicolor,

perhaps due to the excessive sweating but no other mucocu-

taneous lesions. He was moderately nourished and general

physical examination was otherwise normal.

Neurological examination revealed normal higher cogni-

tive functions and Cranial nerve examination including

Fundus were normal. There was no muscle wasting and

there was minimal toe grip weakness. The abdominal reflex

was present and plantars were flexor. The Deep tendon re-

flexes were normal in the Upper limbs, Knee jerks were

reduced and Ankle jerks were not elicitable. There were

intermittent coarse neuropathic tremors involving the left

toes. There was graded sensory loss involving Touch, pain,

temperature, Vibration and position sense below the knee.

The gait was broad based and ataxic and there was marked

worsening of balance on eye closure. There was no nerve

thickening. A diagnosis of predominantly sensory progres-

sive polyneuropathy was made and the patient was

investigated.

Nerve conduction study revealed absent sensory re-

sponses in all four limbs. The motor responses were normal

in the Upper limbs. In the lower limbs, the DMLs were

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borderline, the CMAP amplitudes were reduced and the CVs

were mildly reduced. The Right Tibial f wave latency was

prolonged and the other f waves were normal. The RR in-

terval variability was normal, but the Sympathetic skin

response was absent. The NCS features were suggestive of a

predominantly sensory polyneuropathy with autonomic

neuropathy involving the sympathetic component and the

motor abnormalities pointed to a predominantly axonal

process. The VEP revealed prolongation of the P100 latencies

on either side.

His blood investigations including ESR, CRP and Vasculitis

package were normal. HIV and HTLV 1 and 2 antibodies were

negative.

His MRI Brain and CSF study were normal. His Audiometry

was normal.

A detailed dietary history was undertaken. The patient

said that he has been eating Cassava daily for several years.

The Cassava was boiled, cut into pieces, fried and eaten.

The other family members, though used to consume Cas-

sava, did so about twice a week, where as the patient was

taking it daily, as he was fond of it. He denied that anyone

else in the family or immediate neighbourhood had a

similar illness.

A nerve and muscle biopsy were done. The muscle bi-

opsy from the vastus lateralis showed features of early

denervation without any inflammatory changes. Sural nerve

biopsy revealed shows 3e4 fascicles enclosed by thick

epineurium. There was marked loss of large and small

diameter fibres in all fascicle with several bands of bungner

but no axonal regeneration. The fibre loss was overall uni-

form but focally within fascicle it was in pockets. Few fibres

had thick myelin (architecture) epi and endoneurial small

vessels showed thickening reflecting chronicity. No vascu-

litis was noted. Impression: Chronic axonopathy without

regeneration e consistent with nutritional/Tropical ataxic

neuropathy.

Based on the Dietary history, typical clinical features and

nerve biopsy features a diagnosis of Tropical ataxic neuropa-

thy (TAN) was made. The patient was strongly adviced to stop

consuming Cassava and was prescribed S-adenosyl methio-

nine, neurotropic vitamins and Cap Astymin forte (Essential

Aminoacids).

2. Discussion

Cassava, also called Tapioca or manioc, is a staple food for

over 600 million people around the globe and especially in

the Tropics. The crop variety is a tuber and it is resistant to

drought, plant diseases, insects and animal predators8 and

needs relatively little water to survive and hence represents

an extremely valuable crop for subsistence.9 Cassava con-

tains a cyanogenic compound Linimarin which releases cy-

anide which is neurotoxic.6 Usually cassava is processed by

powdering and drying which helps to reduce the cyanide

content considerably. However, during famine or due to

personal preference, if proper processing is not done, the

propensity to build toxic levels in the body increases. During

famine, when cassava is consumed in large quantities,

leads to a condition called Konzo. Here, there is severe

involvement of the corticospinal tract and patients present

with subacute onset of spastic paraplegia which resembles

Lathyrism. When the toxic dose is small and the exposure is

for a prolonged period, patients develop Tropical ataxic

neuropathy. The incidence of Konzo and Tropical ataxic

neuropathy can be as high as 3% in some places in Africa.

The four cardinal features of Tropical ataxic neuropathy are

1. Severe sensory ataxia, due to involvement of the sensory

ganglion or posterior column. 2. Predominantly sensory pe-

ripheral neuropathy. 3. Optic neuropathy. 4. Sensorineural

deafness.1 The presence of any two of the above with

appropriate dietary history is sufficient to make the diag-

nosis of Tropical ataxic neuropathy. In a study of 206 pa-

tients in Nigeria,9 glove and stocking sensory impairment of

pain and touch sensibilities were found in 202 (98%), sensory

gait ataxia in 172 (84%), optic atrophy in 98 (48%), and

neurosensory deafness in 40 (19%).3 The disease manifested

mostly during the 4th decade, however it can start from 8

years to 60 years of age. In one study Knee jerks were absent

or diminished in 76% of patients and was normal in 24%.4

Vitamin deficiencies did not play a significant role in any

of the studies on TAN,5 but deficiencies of sulphur contain-

ing amino acids (which are essential for detoxifying cyanide)

were found in studies.7

In India, cassava is consumed mainly in Kerala among the

lower socioeconomic strata and Dr Madhusudhan et al have

published a large series of 40 patients with Tropical ataxic

neuropathy. In their series, all had sensory polyneuropathy,

90% had sensory deafness, 50% had visual impairment and

25% had spasticity involving the lower limbs. Increased levels

of thiocyanatewere demonstrated in the Urine, serumor sural

nerve specimens.2

In this era of Medical tourism, whenwe encounter patients

from other countries, it appears essential to have an idea

about the dietary habits and common neurological disorders

prevalent in such countries.

Conflicts of interest

The author has none to declare.

r e f e r e n c e s

1. Dobbs Michael R. Textbook of Clinical Neurotoxicology. 1st ed.Saunders; 2009.

2. Madhusudanan M, Menon MK, Ummer K,Radhakrishnanan K. Clinical and etiological profile of tropicalataxic neuropathy in Kerala, South India. Eur Neurol.2008;60(1):21e26.

3. Oluwole OS, Onabolu AO, Link H, Rosling H. Persistence oftropical ataxic neuropathy in a Nigerian community. J NeurolNeurosurg Psychiatr. 2000 Jul;69(1):96e101.

4. Roman GC, Spencer PS, Schoenberg BS. Tropicalmyeloneuropathies: the hidden endemias. Neurology. 1985Aug;35(8):1158e1170.

5. Osuntokun BO, Aladetoyinbo A, Bademosi O. Vitamin Bnutrition in the Nigerian tropical ataxic neuropathy. J NeurolNeurosurg Psychiatr. 1985 Feb;48(2):154e156.

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6. Makene WJ, Wilson J. Biochemical studies in Tanzanianpatients with ataxic tropical neuropathy. J Neurol NeurosurgPsychiatr. 1972 Feb;35(1):31e33.

7. Osuntokun BO, Durowoju JE, McFarlane H, Wilson J. Plasmaamino-acids in the Nigerian nutritional ataxic neuropathy. BrMed J. 1968 Sep 14;3(5619):647e649.

8. Tshala-Katumbay D, Mumba N, Okitundu, et al. Cassava foodtoxins, konzo disease, and neurodegeneration in sub-SaharaAfricans. Neurology. 2013;80:949e951.

9. Osuntokun BO. An ataxic neuropathy in Nigeria: a clinical,biochemical and electrophysiological study. Brain.1968;91(2):215e248.

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