Lathyrisme

Lathyrism is a disease caused by eating seeds of species of Lathyrus (the grass pea), mainly L. sativus (the chickling pea or khesari), L. cicera (flat-podded vetch) and L. clymenum (Spanish vetchling). It affects mostly people in Bangladesh, India, Pakistan, Nepal and Algeria but is sometimes found in France, Italy, Spain and Australia. This disease affects horses and cattle as well as in man. Beta-oxalyl-amino-L-alanine acid (BOAA), an excitatory neurotoxin and glutamate agonist, has been identified as the constituent of the chickling pea responsible for the disease. BOAA appears to exert its effects through mitochondrial toxicity.¹

The first record of the disease is thought to be an ancient Hindu work called Bhavaprakasa but it was also described by Hippocrates around 400 BC. A survey in India in 1833 reported the disease in poor people during a drought but it was not until 1873 that Cantani in Italy named the disease as lathyrism.

Épidémiologie

The chickling pea flourishes in conditions of both flood and drought, when no other food crop survives. It has been the traditional survival food of the poor in some developing countries. An epidemic in the Gondar region of Ethiopia in the 1970s left 1% of the population permanently crippled.²Victims of the forced labour camps in the Second World War displayed signs of chronic lathyrism following a wartime daily dietary intake of 400 g of L. sativus peas cooked in water plus 200 g bread made of barley and straw.³In more recent years, there has been concern that famine conditions in Afghanistan could produce an epidemic of lathyrism.⁴

It can be boiled as a vegetable, eaten as gruel, or ground into flour to make bread. In the west and north west of Bangladesh, khesari is a staple part of the diet - agricultural labourers eat rutee or chapatee made of khesari. Signs of disease generally appear whenever a diet consisting of one third to one half of L. sativus seed is consumed for 3 to 6 months. Men are affected more often than women, particularly those in the 25-40 year-old age range.⁵

Facteurs de risque⁶

• Cooking with clay implements

• Eating green unripe and boiled pea forms

• Blood group O⁷

Facteurs protecteurs⁶

• Soaking the green peas prior to cooking with fresh water

• Eating with antioxidants or mixed with cereals rich in sulphur-based amino acids

Présentation

• The onset of neurolathyrism is usually sudden and coincident with the monsoon season. Early symptoms include:
  

  • Walking difficulties

  • Unbearable cramps

  • Leg weakness

• Spastic paralysis develops which becomes irreversible.

• Pyramidal tract involvement causes:
  

  • Motor weakness

  • Increased tone

  • A lurching scissoring gait caused by involvement of the thigh extensors and adductors and gastrocnemius

  • Extensor plantar responses

  • Very brisk knee and ankle tendon reflexes, often clonic

  • Hoffmann's sign and exaggerated biceps and/or triceps tendon jerks in the most severely affected

• There are no objective sensory signs but perverse sensations in the legs are frequently reported at the onset. Walking difficulties often begin suddenly but may also appear subacutely or insidiously. Some people experience partly reversible symptoms suggestive of a diffuse CNS excitation of somatic, motor and autonomic function.⁸Spasticity can be more marked than the motor weakness.⁹

• Lathyrism is not simply a paralytic syndrome, as angiolathyrism causes sudden death: the toxin changes the elasticity of the aorta causing anévrisme aortique that may rupture.

• Osteolathyrism affects skeletal development: cartilages and bones grow abnormally leaving the body deformed.³Children suffer skeletal deformity and poor cerebral development.

Diagnostic différentiel

Other causes of hypertonic paraparesis - for example:

• Pott's paralysis

• Konzo

• HTLV-1 infection

Gestion

The disease is usually nonprogressive but irreversible. Tolperisone, a centrally acting muscle relaxant, has been shown to produce significant reduction in the spasticity in neurolathyrism patients.¹⁰Other than that there is remarkably little in the literature about the drug treatment of the condition.

Prévention

Public health education about the dangers of lathyrism is obviously important but the harsh reality is that people may face a choice between lathyrism or starvation. Food preparation measures can help:

• Boiling in water or repeated steeping in hot water and discarding the extracts can detoxify the seeds.

• Roasting the seeds at 140║C for 15 to 20 minutes results in 80-90% destruction of the neurotoxins.

• Soaking the seeds or dhal overnight and decanting the water before cooking eliminates about 90% of the toxin.

The dangers of lathyrism are often known along with knowledge of how to detoxify Lathyrus but drought conditions can lead to fuel and water shortages preventing the necessary steps from being taken.

One goal for prevention is to develop a plant with the resilience of chickling pea to extreme climatic conditions, with its nutritional content and taste but without toxin ('zero BOAA' strains). Genetic modification could offer safer food and the utilisation of marginal farming land. Some varieties of chickling pea that contain a much lower amount of toxin have been developed and may become more widely cultivated.¹¹