Elsa C. Raimondi

The morbid processes that fall under the name of polyneuropathies are among the most frequent and widespread affections of the human being. They can develop in all races, ages and in both sexes, and in at least an appreciable proportion of cases they are related to environmental and industrial factors created by man in his constant progress.

The term designates those pathological processes that affect segments of the peripheral nervous system, that is, derived from the second motor neuron, the first sensory neuron and neurons of the peripheral autonomic nervous system (anterior and posterior roots, root ganglia dorsal, nerve trunks and their ramifications) simultaneously, symmetrically and persistently.

The spinal nerves are commonly involved, and the cranial nerves are often involved; rather, these are part of the group of mononeuropathies, also frequent but limited to one nerve. Also noteworthy are multiple mononeuropathies that damage several nerves that are distant from each other (there is no symmetry) and that, in general, are not affected simultaneously

Polyneuropathies can be the only manifestation of the disease or they can be integrated into more generalized pictures of systemic diseases and, given the multiple factors that can cause them and that sometimes escape the usual or available diagnostic procedures, it is that in a percentage of cases (around 15%, depending on where they are studied) remain without an etiological diagnosis.

Since the peripheral nerves are made up of the extensions of neurons, by the Schwann cells and the myelin sheaths that these cells make, by the connective tissue that surrounds the fibers and by the blood vessels, it will be understood that the acting pathologies they may be directed against any one of those components in particular and that the persistence of noxa may secondarily alter the other elements.

All these concepts have determined that polyneuropathies are classified in various ways, attending in each case to the etiology, pathology, clinic, and evolution. As the symptoms and signs of polyneuropathies differ slightly despite the different responsible etiologies, to reach the diagnosis of the cause it is important to take into account certain factors that facilitate the investigation and are the following: a) age of onset : there are cases of beginning in childhood or adolescence, as is the case with hereditary neuropathies; b) temporal pattern of presentation: in this sense it is indicative to know if the evolution of symptoms has been acute (up to 4 weeks) as in the case of Guillain-Barré Syndrome and polyneuritis of porphyria among others, subacute (4 to 8 weeks) as in some toxic, metabolic and autoimmune, chronic (greater than 8 weeks) as in that associated with diabetes, alcoholism and paraneoplastic or recurrent as in chronic inflammatory demyelinating polyneuropathy; c) Symptom distribution : it should be evaluated if the symptoms are only distal or distal and proximal and if they are symmetric or asymmetric (multiple mononeuritis).

Symptoms and signs

The clinical picture will depend on the predilection that noxa has for any of the components of the nerve (axon, myelin, motor, sensory and / or vegetative fibers) and on this basis the symptoms may vary; in any case, this variability falls within a narrow margin of symptoms.

This is how the disease can manifest itself by sensory, and / or motor, and / or vegetative disorders.

Main clinical forms

Distal motor sensory polyneuritis : the vast majority of neuropathies present in this form and its cause is usually metabolic, toxic, or hereditary. It begins with subjective sensations of tingling, numbness, burning and / or pain in the distal parts of both lower limbs, simultaneously and symmetrically. These sensitive symptoms can be located there in mild cases or:

a) continue ascending towards the root of the lower limbs;

b) affect the distal portions of the upper limbs with the same paresthetic symptoms;

c) add motor symptoms, also distal and more frequently in the lower limbs, but also in the upper limbs;

d) add symptoms of vegetative dysfunction at any time.

The muscular weakness that occurs is a consequence of the affection of the muscles of the antero-external group of the legs, which has as a consequence the difficulty in the dorsiflexion of the feet (equine gait or steppage occurs). If the evolution continues, weakness of other muscles occurs, such as the calves and soleus. In the upper limbs, motor dysfunction is initially translated by difficulty in the movements of the hands. The mentioned paresis are accompanied by muscular atrophy in the sectors involved and can become accentuated. The objective examination of the sensitivity will show the presence of hyperesthesia, generally in its initial stages and then of tactile, thermal and painful hypoesthesia in the distal parts of the limbs, in the form of a boot and glove. A decrease in vibratory sensation to the tuning fork (distal hypopaesthesia) can also be seen. In the state period, the tendon reflexes are diminished or absent. The involvement of the autonomic nervous system results in anhidrosis, sexual impotence, orthostatic hypotension, as the most frequent.

Sensory neuronopathies : in this type of neuropathy, the thicker sensory fibers are affected. It manifests simultaneously, symmetrically and both distally and proximally and under the symptoms of severe proprioceptive sensory ataxia with areflexia. The cause may be pyridoxine, cisplatin poisoning, or as a paraneoplastic expression.

Polyneuropathy of fine sensory fibers : (in its evolution the thicker fibers are usually compromised). It occurs distally with paresthesia, dysesthesia, burning or burning, and sometimes they are so intense that they prevent the patient from resting their feet on the ground and at night, when the symptoms worsen, the mere friction of the sheets becomes unbearable for the patient. This clinical pattern can be observed in neuropathies due to diabetes, amyloidosis, HIV and toxic

Distal and proximal symmetric motor polyneuropathy with minor sensory disturbances: This is the most typical presentation pattern of autoimmune demyelinating neuropathies, that is, Guillain-Barré syndrome and the chronic relapsing form. In the case of the first of those mentioned, although it presents subjective and objective sensory symptoms, they are mild and are quickly relegated and overcome by the great motor compromise that, beginning in most cases in the lower limbs, progresses from ascending and rapid way, being able to stabilize at any level or advance enough to leave the quadriplegic patient with the possibility of having respiratory disorders. Even cranial nerves such as the facial, bulbar motors and oculomotor nerves may be involved. Generalized areflexia and flaccidity are established early on.

It is necessary to take into account that the same cause, for example, diabetes, can present in different clinical forms, as can be seen in the following diagram of the main peripheral neuropathies.

The toxic causes of polyneuropathies include those caused by industrial or environmental poisons such as: trichlorethylene, heavy metals, acrylamide, aniline, carbon compounds, dinitrobenzole, dinitrophenol, ketones, DDT, orthocresyl phosphate and by drugs that have deleterious effects on the peripheral nerves, such as: amiodarone, dapsone, disulfiran, glutethimide, isoniazid, lithium, metronidazole, nitrofurantoin, sulfamides, thalidomide, vincristine, chloramphenicol among the best known.

Among the hereditary polyneuropathies, the most common are: Charcot-Marie-Tooth disease, Dejerine-Sotas disease, Refsum disease, Roussy-Levy disease, Tangier disease, Riley-Day disease. The study of these neuropathies is beyond the scope of this book

There are some polyneuropathies that present a clinical picture with certain characteristics of a general or particular order that stand out from the rest, as is the case of lead neuropathy (lead poisoning). In this case, there is a manifest predilection for the motor nerves of the upper limbs, in particular, the radial nerve, giving rise to the "pendulous hand". As general symptoms, it presents abdominal pain and constipation, pigmented gingival ridge, anemia and basophilic stippling in the blood precursors of the bone marrow.

Study methodology

Taking into account the semiological characteristics, the diagnosis of polyneuropathy is easy. On the other hand, the study of the possible etiologies is much more laborious and even using all the available methods, currently the cause can remain without finding the cause in 15% of the cases. The investigation of the patient with polyneuritis requires a thorough interrogation looking for family history, exposure to toxins, consumption of medications, metabolic, nutritional, infectious diseases, etc. Because alcoholism is a very frequent habit in our country and because diabetes is one of the most prevalent diseases, these two are the main causes of polyneuritis. Added to them is the acute inflammatory demyelinating polyneuropathy (Guillain-Barré syndrome). In general, the diagnosis of them emerges immediately. For the rest, it is often necessary to have the collaboration of different specialists. Following the examination of the patient, one should proceed according to the orientation given by the main clinical forms. The pertinent blood and urine tests should be requested and in all cases an electromyogram should be performed with a study of motor and sensory conduction velocity. This method will allow to differentiate the diseases of the nerves from others that are not; discriminate if the lesion affects the axon or myelin, locate the site (nerve, plexus, etc.); indicate symmetry and chronicity. Nerve biopsy is a study of little use in investigating the cause of neuropathy. The main indication is the identification of vasculitis, sarcoidosis, amyloidosis, leprosy. The nerve to perform the biopsy is the sural at the ankle level. Cerebrospinal fluid study is indicated to evaluate acute and chronic dysimmune demyelinating polyneuropathies. In these cases, the CSF shows an albumin-cytological dissociation in 90% of the patients.