Neurogenic Bladder: UMN vs LMN: Physiology made easy.

Basic Physiology of Micturition

Micturition is a spinal reflex modulated by CNS.

Neural control of micturition.
Source: http://physiologyplus.com/micturition-reflex-steps/

The pre-frontal cortex is responsible for the cognitive control of the micturition which analyses the signals from bladder and conveys signals according to void or not to void depending on the social setting.

The higher control of micturition is mediated by pontine micturition centre (PMC) from where nerve fibre arise and travel along the lateral columns bilaterally. It is the mechanical control of micturition. It coordinates the function of baldder and sphincter.

The Sympathetic fibres are thoracolumbar (T10-L2) outflow of nerve fibres and terminate in the hypogastric ganglion.

The Parasympathetic fibres are sacral (S2-S4) outflow.

The voluntary control over the external urtheral spincter is mediated by somatic fibres of Pudendal nerve. 

Learn about Cranial nerve examinations

Intact Spinal cord is essential for normal micturition as it serves as a intermediate relay between the brain and the sacral center of micturition. Sacral reflex center is the primitive voiding center which is responsible for infants diaper need, since there is a continuous cycle of bladder filling and voiding. The higher mental function gradually enhances in kids as they are growing and accordingly they are trained to use toilet with their enhanced higher mental function.

	Sympathetic	ParaSympathetic
Bladder (Detrusor Muscle)	Relaxation	Contraction
Bladder Neck	Contarction	Relaxation

The bladder wall is relaxed and the neck constricted with sympathetic stimulation which allows for retention of urine. The parasympathetic stimulation causes bladder wall to contract and sphincter to relax easing the voiding of urine.

Learn about the analogy of skeletal muscle and bladder in UMN and LMN lesions. 

Analogy of Skeletal Muscle contraction and Bladder

LMN vs UMN Lesion : Effect on Bladder

There is a lot of analogy between skeletal muscle contraction and bladder.

In the absence of higher control, overdistension of bladder causes reflex detrusor contraction. Similar to     the muscle stretch reflex mediated by spindle fibre in skeletal muscle.

The upper motor neuron lesion of the brain and the spinal cord causes features similar to that of the UMN lesion of in the muscle characterized by Spastic bladder/ Hypertonic baldder.This is due to the reflex detrusor contraction. There is increased tone of the detrusor muscle. However, the bladder contracts with overdistension, the sphincter does not relax causing bladder sphincter dyssyenrgia. This causes urgency and urge incontinence. The volume of residual urine in the bladder is increased which causes high risk for UTI and chronic renal failure due to obstructive uropathy. The site of the lesion is generally the Spinal cord or pons or higher. There is no gross dilatation of the bladder due to the reflex contraction which results in low volume high pressure inside the bladder.

Learn about the plantar reflexes and its variants with video demonstration

The lower motor neuron lesion to the fibre supplying bladder causes overflow incontinence. This occurs because bladder is overdistended however the reflex detrusor contraction doesnot comes into play. So what happens is the bladder leaks over time when it is beyond its holding capacity without the detrusor muscle contracting. The bladder is grossly dilated resulting in high vomule and low ressure inside the bladder.This can be described as flaccid or atonic bladder similar to flaccid paralysis of muscles in LMN lesion.The patient cannot initiate the micturition. The site of injury is generally the sacral fibres or peripheral nerve fibres

The last type of neurogenic bladder ocuurs due to injury in the prefrontal cortex which is responsible for social control of micturition. It allows us to find us to micturate in appropriate place. The patient doesnot have the sense of bladder fullness. They have trouble initiating micturition and they micturitate at inappropriate places.

Character	UMN Type	LMN Type
	Spastic Bladder	Flaccid Bladder
Tone	Hypertonic (Increased)	Hypotonic (Decreased)
Volume	Normal or small	Large
Detrussor contraction	Involuntary intermittent contractions (Overactiity)	Absent (Underactivity)
Pressure	High	Low
Incontinence type	Urge	Overflow
Symptom	Urgency and Frequency nocturia Leaking of urine	Dribbling of urine Erectile edysfunction in men
Retention	Incomplete bladder voiding (Detrussor-Sphincter Dyssynergia) Uncoordinated bladder contraction and sphincter relaxation	Detrusor Aflexia
Conditions	Spinal Cord damage above T12 Cerebrovascular accidents	Spinal cord damage at S2-S4 Peripheral Nerve injury Acute Stage of spinal cord injury Cauda Equina, Conus medullaris

  

Source: Davidson, Merck’s Manual, Medscape

Sensitivity, Specificity, PPV, NPV

Sensitivity is TRUE POSITIVE RATE.

2x2 table 

Sensitive test picks all diseased and also sometimes without disease. That means it won’t miss the disease.

Sensitivity is a measure of  test positive out of total diseased. 

Specificity is TRUE NEGATIVE RATE.

Specific test picks only the diseased one but may sometime miss the disease itself.

Sensitivity and specificity are not dependent upon the disease prevalence rate.

Specificity is measure of true negative out of total healthy patient. 

Predictive values depend upon the prevalence of disease and accuracy of the test.

Positive Predictive Value is the proportion of the people with positive test who actually have disease.

Negative Predictive Value is the proportion of the people with negative test who actually do not have disease.

	PPV	NPV
Definition	% that a person with positive test is actually diseased.	% change that a person with negative test is actually disease free.
Use	Proceed with a patient with positive test	Proceed with a patient with negative test
Relation to prevalence	Low prevalence low PPV High prevalence high PPV	High prevalence low NPV Low prevalence High NPV

Difference between temporal bone fracture types: Longitudinal Vs Transverse: Made Easy

The temporal bone fracture are common with head injury accounting for 30 % of all head trauma and 75 % of all motor vehicle accident. 31% of temporal bone fracture are associated with Motor vehicle accident. 

Longitudinal fracture are common fracture caused by lateral forces over the mastoid and temporal squamosa and fracture line parallels petrous pyramid axis. It is generally anterior and extra-labyrinthine.

NEURAL SYMPTOMS WITH TRANSVERSE #

PHYSICAL SYMPTOMS WITH LONGITUDINAL #

Difference between temporal bone fracture types: Longitudinal Vs Transverse

Nerve Injury or neural component more common with transverse # Facial nerve injury(VII), vertigo(VIII: Vestibular Nerve), Sensorineural hearing loss(VIII: Auditory Nerve) and Nystagmus (vestibular Nerve/ CNS component) are more common and intense with transverse fracture.

Physical damage like bleeding demonstrated as  Hemotympanum and otorraghia , fractures seen as  CSF otorrhea, Conductive hearing loss due o disruption of ossicles and Tympanic membrane perforation, are common with longitudinal fracture. Neural component less common or less intense than it’s contrary.

Differential diagnoses of various otological symptoms

Parameter		Longitudinal Fracture	Transverse Fracture
Direction Of  Fracture		Along The Axis Of Petrous Pyramid	Perpendicular To Petrous Pyramid
Incidence		More Common (80%)	20%
Mechanism		Parieto Temporal Trauma	Fronto Occipital Trauma
Otoraghia	PHYSICAL DAMAGE	Common	Rare
Hemotympanum		Common	Possible
TM Perforation		Common	Rare
CSF Otorrhoea		Common	Occasional
Hearing Loss		Conductive	Sensorineural	NEURAL DAMAGE
Facial Nerve Injury		Less Common (20%) Often Temporary Delayed Onset	More Common (50%) Often Permanent Acute Onset
Vertigo		Common (Less Intense)	More Intense
Nystagmus		Common (Less Intense)	Common Third Degree