Epiconus Syndrome

Anatomically, the epiconus comprises the cord segment between L4 and S1, corresponding to the T12 and L1 vertebrae. The conus medullaris consists of the cord segment between S2 and S5 as well as coccygeal segments. The lumbosacral nerve roots are collectively termed the cauda equina wihch runs laterally and distally to the epiconus as well as the conus medullaris.

A lesion of the epiconus (L4 to S1 spinal cord segments) can produce, as weakness develops, a flaccid type paralysis with signs of lower motor neuron involvement. When the lesion involves the spinal cord above the epiconus, spastic paraesis as a sign of upper motor neuron dysfunction may also occur. Similarly, when the lesion involves the cord distal to the epiconus, bladder dysfunction, as a sign of conus medullaris compromise, and the cauda equina syndrome is usually evident on clinical presentation.

The epiconus syndrome presents with the following clinical features.

(1) A sensory disturbance in the leg (transverse, saddle, radicular, or socks type).

(2) Motor deficit as a sign of lower motor neuron involvement (foot drop, fasciculation, muscle atrophy).

(3) Diminished deep tendon reflexes.

(4) Occasional coexistence of positive pathological reflexes (Babinski's and Chaddock's signs).

(5) Diminished vibration sensation, and

(6) Bladder and bowel dysfunction.

In the presence of a dysfunctional conus medullaris, sensory disturbance in the perineal area (usually saddle type) and diminished vesicourethral as well as anorectal reflexes are significant findings. On the other hand, no significant abnormalities of voluntary leg movement and in deep tendon reflex activity are observed.

The cauda equina syndrome is a well recognised clinical entity with a flaccid type of paresis and/or intermittent neurogenic symptoms, and infrequently, parasympathetic disorders with unusual symptoms of penile erection as well as urinary incontinence.

The differential diagnosis should include old poliomyelitis, tethered cord syndrome as well as spinal dysraphism, amyotrophic lateral sclerosis, hereditary spastic paraplegia, hereditary sensorimotor neuropathy (Charcot-Marie-Tooth; Dejerine-Sottas), and spinal progressive muscular atrophy (Kennedy-Alter-Sung).