Examen neurológico de los miembros inferiores

Existe más de una forma de realizar una exploración neurológica y el clínico debe desarrollar su propia técnica. Una técnica deficiente puede hacer que no se obtengan signos o producir resultados falsos.

See the separate Neurological History and Examination article which covers the basic principles of examination and technique.

Inspection of the lower limbs¹

Note whether there is any damage to the feet. Neuropathic ulcers and neuropathic joints develop because of a lack of pain perception. Pain is a protective mechanism. When inspecting the motor system, the following points should be assessed:

• Note the resting posture. Establish whether there is unusual rotation or posture of a joint. Note whether the patient is symmetrical.

• Look for muscle wasting or hypertrophy: note whether it is focal or diffuse.

• Busque movimientos involuntarios como temblores, tics, sacudidas mioclónicas, corea o atetosis.

• Look for muscle fasciculation (a sign of lower motor neurone disease process). These are subcutaneous twitches over a muscle belly at rest. Tapping the belly may stimulate fasciculation.

Lower limbs examination of the sensory system

Examination of the lower limbs may be performed more easily with the patient lying on a couch.

Examination of each of the sensory modalities¹

Toque ligero

• Utiliza los ligeros toques de un dedo, un trozo de algodón o un trozo de papel de seda.

• Es importante tocar y no acariciar, ya que una sensación de movimiento, como el roce y el rascado, se conduce por las vías del dolor.

• Pide al paciente que cierre los ojos y te diga cuándo siente que le tocas.

• Compara cada extremidad en la misma posición.

• Mantén el ritmo de cada toque irregular para evitar la anticipación del paciente.

• A logical progression is required. You may want to start testing over the groin and to move down the front of the leg and up the posterior side as this moves progressively from L1 to S3 dermatomes.

• Anote cualquier zona de hipoestesia o disestesia.

Tacto agudo (pinchazo)

• Realice la prueba con una aguja desechable específica. Una aguja hipodérmica desechable está demasiado afilada.

• Utilice la zona del esternón para establecer una línea de base para la nitidez antes de empezar.

• Follow the same progression as with light touch with the patient's eyes closed, comparing both lower limbs.

• Pida al paciente que indique si tiene hipoestesia (sensación de mayor embotamiento) o hiperestesia (sensación de mayor agudeza).

Temperatura

• A menudo se pasa por alto, pero puede ser importante.

• An easy and practical approach is to touch the patient with a tuning fork, as the metal feels cold.

• Compare la calidad de la sensación térmica en brazos, cara, tronco, manos, piernas y pies.

• Pueden utilizarse recipientes con agua caliente y fría para una evaluación más precisa. Pida al paciente que distinga entre agua caliente y fría en distintas zonas de la piel con los ojos cerrados.

Sentido de la posición articular (propiocepción)

• Test at the interphalangeal joint of the big toe.

• Hold the proximal phalanx with one thumb and finger and hold the medial and lateral sides of the distal phalanx with the other. Move the distal phalanx up and down, showing the patient the movement first.

• Pida al paciente que cierre los ojos y mueva la falange distal hacia arriba y hacia abajo de forma aleatoria. Pídele que te diga la dirección del movimiento cada vez.

• Test on both feet.

• If there is an abnormality, move backwards to the metatarsophalangeal joint and so on until joint position sense is normal.

Sentido de la vibración

• Utilice un diapasón de 128 Hz y asegúrese de que vibra.

• Para empezar, colóquelo en el esternón para que el paciente perciba la sensación.

• Then place it on the big toe.

• If no vibration is sensed, move backwards to the bony malleolus of the ankle, the tibial shaft and tuberosity and the anterior iliac crest.

• Pedir al paciente que le diga cuándo deja de vibrar el diapasón puede ser útil si hay dudas de que su sentido de la vibración esté intacto.

2-point discrimination

• This test is not usually performed on the soles of the feet because the distinguishing distance is usually much greater than that on the fingers.

Interpretación de los resultados

The site of any lesion can be determined by looking at the pattern of any dysfunction found. The dermatomal (segmental) and peripheral nerve innervation is labelled below.

Examen neurológico

Häggström, Mikael (2014). "Galería médica de Mikael Häggström 2014". WikiDiario de Medicina 1 (2). DOI:10.15347/wjm/2014.008. ISSN 2002-4436. Dominio público

• All of the sensory modalities can be affected in peripheral neuropathies and nerve injuries, radiculopathy due to disc lesions and spinal injuries.

• Si se ve afectado un nervio individual o una raíz sensorial, pueden reducirse todas las modalidades sensoriales.

• If there is a spinal cord lesion, there may not be equal diminution across all of the sensory modalities: light touch, vibration and joint position sense may remain intact while sharp touch and temperature are lost. This is because the lateral spinothalamic pathways may be damaged while the dorsal columns remain intact.

• Problems with joint position sense or vibration usually occur distally first. Joint position sense is also required for balance, gait and co-ordination.

• El sentido de la vibración puede perderse antes que el sentido de la posición articular en caso de neuropatía periférica o mielopatía que afecte a las columnas dorsales.

• Vibration sense over the ankles is often diminished or lost in elderly people with no apparent neurological lesion.

• Las partes distales de las extremidades tienden a verse afectadas en la polineuropatía, afectándose normalmente las piernas antes que los brazos. Se produce un efecto de "guante y media".

Lower limbs examination of the motor system²

Tono

• Tone is the resistance felt when a joint is moved passively through its normal range of movement. Hypertonia is found in upper motor neurone lesions; hypotonia is found in lower motor neurone lesions and cerebellar disorders.

• Clonus is rhythmic and involuntary muscle contraction that can be provoked by stretching a group of muscles.

• Test tone:

  • Ask the patient to let their legs 'go floppy'.

  • Internally and externally rotate the 'floppy' leg. Assess for any increased or reduced tone.

  • Then lift the knee off the bed with one of your hands. Note whether the ankle raises off the bed as well, signifying increased tone.

• Test for ankle clonus:

  • Flex the patient's knee, resting the ankle on the bed.

  • Dorsiflex the foot quickly and keep the pressure applied.

  • You will be able to see the foot moving up and down if clonus is present.

Potencia

• Se requiere una evaluación sólida de la potencia.

• El Consejo de Investigación Médica (MRC) dispone de un sistema de clasificación recomendado para la potencia (véase la tabla). Se ha demostrado que tiene una buena fiabilidad, aunque se han expresado dudas sobre la amplia gama de grados 4³ .

• La prueba muscular manual se puntúa de forma diferente con 4 - Bueno: ROM completo contra la gravedad con resistencia moderada, y 5 - Normal: ROM completo contra la gravedad con resistencia máxima.⁴ .

• Get the patient to contract the muscle group being tested and then you as the examiner try to overpower that group.

• Prueba lo siguiente:

  • Hip flexion, extension, adduction and abduction.

  • Knee flexion and extension.

  • Foot dorsiflexion, plantar flexion, eversion and inversion.

  • Toe plantar flexion and dorsiflexion.

Escala MRC de potencia muscular

Reflejos tendinosos profundos

• Asegúrese de que el paciente está cómodo y relajado y de que usted puede ver el músculo que se está probando.

• Utilice un martillo para tendones para golpear el tendón del músculo y busque la contracción muscular.

• Compara ambos lados.

• Los reflejos pueden ser hiperactivos (+++), normales (++), lentos (+) o ausentes (-). ± se utiliza cuando el reflejo sólo está presente en el refuerzo (véase más adelante).

• In the lower limbs:

  • Test the knee jerk (L3, L4): flex the patient's knee and support it by using one of your hands in their popliteal fossa. Elicit the reflex by tapping just below the patella.

  • Test the ankle jerk (S1): with the patient lying down, flex their knee and dorsiflex their ankle, at the same time rotating their leg slightly laterally. Elicit the reflex by tapping over the Achilles tendon just above the heel. If this is difficult to elicit, an alternative method is to ask the patient to kneel on a chair, facing the back of the chair, so that their feet are dangling off the seat of the chair. Tap over the same area in this position.

• If a reflex is difficult to elicit, try 'reinforcement' (the Jendrassik manoeuvre). Ask the patient to flex their fingers and interlock them with one palm facing upwards and the other facing downwards. Then ask them to try to pull their fingers apart just before you strike the tendon.

Interpretación

• Las lesiones de la neurona motora superior suelen producir hiperreflexia.

• Las lesiones de la neurona motora inferior suelen producir una respuesta disminuida o ausente.

• It may be normal to have reduced or absent ankle reflexes in some elderly people, although the frequency and significance of this is disputed.

• Isolated loss of a reflex can point to a radiculopathy affecting that segment - eg, loss of ankle jerk if there is an S1 disc prolapse.

Superficial tendon reflexes

• In the lower limbs, this is the plantar response.

• To elicit this, the patient should be lying down with their legs extended.

• Use a blunted point and run this along the lateral border of the foot, starting at the heel and moving towards the big toe.

• Stop on the first movement of the big toe.

• An extensor plantar response (upgoing big toe) is pathological and signifies an upper motor neurone lesion.

Examen de la coordinación

• The cerebellum helps in the co-ordination of voluntary, automatic and reflex movement. Tests of cerebellar function in the lower limbs require normal power, tone and sensation to be valid and include:

• The heel-shin test:

  • Ask the patient to lift one of their legs and flex it at the knee, keeping the other leg straight.

  • They should then place the heel of the flexed leg on the knee of the other leg and run it down the shin towards the ankle and back again towards the knee.

  • Ask them to repeat this a number of times.

• The heel-toe test:

  • This tests balance mechanisms that rely on the cerebellar, vestibular and proprioceptive systems.

  • The patient either needs to be barefoot or wearing flat shoes.

  • They should walk in a straight line so that the heel of the second foot touches the toes of the first foot. This should be repeated so that the heel of the first foot then touches the toes of the second foot, etc, each time with the patient moving forward.

  • Look at how well they are able to perform this. Is there any staggering which would suggest a lesion of the cerebellum?

• Romberg's test:

  • This also tests balance mechanisms that rely on the cerebellar, vestibular and proprioceptive systems.

  • Ask the patient to keep their eyes open and stand with their feet together, arms by their sides.

  • Then ask them to maintain this position when they close their eyes.

  • Patients who have cerebellar lesions often cannot stand in this position, even with their eyes open. If balance is only lost when the eyes are closed, this signifies a proprioceptive or vestibular lesion.

  • Be ready to catch the patient by standing behind.

Examining the lower limbs and gait

• No neurological examination, especially of the lower limbs, is complete without observing gait.

• This is an enormous topic and there are separate articles discussing Abnormal Gait and Gait Abnormalities in Children.

• Also, watch the patient as they rise from the chair to walk and note any abnormality of movement.