Introduction

• Definition: urinary bladder atony is the inability to effectively contract the bladder resulting in excessive urine storage and incomplete urine voiding. 
• Causes: include L7-S3 spinal cord diseases causing a ‘lower motor neuron bladder’, injuries to the pelvic nerve within the cauda equina (intra and extradural nerve roots) and pelvic nerve within the plexus, bladder overdistension (leading to neuro-muscular junction damage) from urethral obstruction such as urolithiasis, neoplasia, prostatic disease, urethral inflammation, and obstructive feline idiopathic cystitis. Congenital abnormality includes spina bifida. 
• Signs: increased frequency of small volume urination, urine overflow or leaking, urine scaling, persistent or recurrent urinary tract infections.  
• Diagnosis: palpation of a bladder that is flaccid and easy to express, imaging and cystometry for definitive diagnosis. 
• Treatment: manual expression, urethral catheterization, cystostomy tube placement, medical treatment with bethanecol. 
• Prognosis: variable depending on the underlying cause. 

Pathogenesis

Etiology

• Overdistension caused by mechanical or functional outflow obstruction damages the detrusor muscle by interrupting the tight junctions that connect to the smooth muscle fibers leading to ineffective or absent contractions. With prolonged, excessive distension, bladder atony can develop.
• Causes include: 
  • Behavioral (eg pain following pelvic fractures Pelvis: fracture). 
  • Urethral obstruction Urethra: obstruction (eg urolithiasis Urolithiasis, extra / intra-luminal neoplasia Urethra: neoplasia, prostatic disease, urethral inflammation, obstructive feline idiopathic cystitis Idiopathic cystitis). 
  • Cats with upper motor neuron bladders (spinal cord injury cranial to L7) rarely reach a state of distension sufficient to cause bladder atony, although it is in theory possible. In the early stages, without manual expression, bladder overflow is more likely. In later stage, small unsynchronized detrusor muscle contractions can occur which results in a bladder with a reduced storage volume.  
• Lesions in the sacral spinal cord segments (S1-S3), sacral nerve roots (intra versus extra-dural) and pelvic plexus abolish the detrusor reflex (areflexia) resulting in detrusor atony: 
  • Detrusor areflexia with normal urethral sphincter tone is caused by damage to the pelvic plexus without damage to the pudendal nerve. It may occur following a traumatic injury to the pelvis and with some spinal cord or brainstem lesions. 
  • Detrusor areflexia with reduced or absent urethral sphincter tone are caused by lesions affecting the sacral spinal cord segments or sacral nerve roots. The perineal reflexes are diminished/absent in these scenarios.  
• Dysautonomia Feline dysautonomia is a generalized autonomic nervous system failure and can be associated with bladder distension. Urinary tract signs are more common in dogs than cats. 
• Spina bifida Spina bifida is a congenital abnormality of the neural tube during embryogenesis, most commonly found in the lumbo-sacral and sacro-caudal spinal cord segments. Lesions that involve the sacral and caudal nerves can result in urinary and fecal incontinence. The Manx Manx cat breed is overrepresented due to their lack of tail, but overall occurrence is low in cats.

Diagnosis

Treatment

Prevention

Outcomes