What is the bladder and pelvic floor function in neuromuscular disorders?

Updated: Aug 08, 2019
  • Author: Frances M Dyro, MD; Chief Editor: Robert A Egan, MD  more...
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Bladder and sphincter dysfunction are seldom seen, even in advanced neuromuscular disease. The sparing of cells in the Onuf nucleus appears to limit the loss of fibers in the external urethral sphincter and the pelvic floor in general. [12]

Sphincter muscle abnormalities can usually be explained by other factors. This was the case in a group of children with neuromuscular disorders studied by Dyro and Bauer: a child with myotonic dystrophy had no myotonic discharges in the sphincter. [13] They also studied 3 boys with Duchenne muscular dystrophy (DMD), 2 girls with congenital myopathy, a girl with Charcot-Marie-Tooth disease type II, and a boy with Kugelberg-Welander syndrome (KWS).

Motor units in the sphincter of 1 of the girls with congenital myopathy were of low amplitude; another had evidence of denervation after scoliosis surgery. [13] The boy with KWS had some increased-amplitude motor units and uninhibited detrusor contractions attributed to coexisting thoracolumbar syringomyelia. Two of the boys with DMD had detrusor-sphincter dyssynergia, but one had concomitant cerebral palsy and the other had a T10 paraplegia following scoliosis surgery.

Sporadic reports of pelvic floor involvement in neuromuscular disorders have been published, suggesting again that these abnormalities are the exception rather than the rule. Dixon et al reported a 48-year-old woman with limb-girdle muscular dystrophy who had had stress incontinence since the age of 12 years. [14] She was aged 33 years when she developed lower limb weakness and was diagnosed with dystrophy.

Results of EMG in the patient’s limbs were consistent with myopathy. [14] Although she was nulliparous, she had pelvic floor descent. The results of external urethral sphincter electromyography (EMG) were normal, and she had no detrusor hyperactivity. Biopsy of pelvic floor muscles showed combined hypertrophy and atrophy of fibers, with 40% containing 1 or more internal nuclei. Type I fibers predominated.

Bernstein et al studied 10 patients with myotonic dystrophy, with inconsistent results. [15] The investigators used surface electrodes to study the pelvic floor. Four of the patients were infrequent voiders, 1 had urge and stress incontinence, 2 had only urgency, 1 had urinary obstruction, and 2 had “normal” voiding. Sphincter EMG findings were reported as normal in the 9 patients who underwent the test.

In the anterior horn cell disorders—amyotrophic lateral sclerosis, KWS, and polio—little or no compromise of the sphincter is noted, and autopsy evidence indicates that the cells of the Onuf nucleus are spared.

Myasthenia gravis apparently has little effect on the sphincteric mechanism. Greene et al [16] and Wise et al [17] investigated patients with postprostatectomy incontinence and myasthenia gravis and found no influence on the cholinergic receptors of the detrusor by the myasthenia.

Christmas et al described a 59-year-old woman with a 35-year history of myasthenia who had difficulty voiding, a feeling of incomplete emptying, and frequency but whose symptoms improved when she increased her dose of pyridostigmine. [18] A urodynamic study showed normal bladder volume and normal sensation but poor detrusor contractions.

Neuropathies, in particular metabolic neuropathies (eg, those due to diabetes or uremia), do affect sphincter and pelvic floor function. This can be simply a denervation of the motor efferents to the sphincter and pelvic floor, or it can be a combined somatic and autonomic neuropathy. Measurement of the sacral reflex arcs of patients with diabetes or other neuropathies, including hereditary sensorimotor neuropathies, has shown denervation of the sphincters and prolongation of pudendal nerve latencies and latencies of the sacral reflex arc.

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