Potential CAUSES for failure to use litterbox

Medical problems

diarrhea (many causes)

small intestinal- soft to watery
colitis (inflamed colon)- mucus in stool, blood, straining

urinary bladder inflammation
FUS
Bacterial infections
trauma
calculi (bladder stones)
tumors

polydipsia/polyuria
(excessive water volume consumed and urine voided: upper water intake for cats is 1oz/lb; most cats drink considerably less than this)

diabetes insipidus
diabetes mellitus
kidney disease
liver disease
adrenal gland disease
pyometra (pus in the uterus)
hypercalcemia (high blood calcium)
others

Territorial marking

intact female in heat
intact male spraying
marking of peripheral walls particularly near windows may be from presence of outdoor cats
may be triggered by over-crowding of indoor cats
previously neutered cat has a bit of testicular or ovarian tissue remaining, possibly resulting in a low level of hormone which could trigger marking
neutered male with sexual experience exposed to female in heat

Treatment:
neuter all cats (check history of neutered cats; retained testicle in male or signs of heat in female)
prevent other cats from coming around outside of house, close windows, blinds, and doors
prevent overcrowding in multi-cat households
Litter box problems
provide a box for each cat
change litter daily
provide constant access to a box
go back to previously used brand of litter and/or discontinue new disinfectant
move box to where it was previously used
eliminate new or frightening noise near litterbox
move food and water away from litterbox
if cat is only going in one spot, put the litterbox at the exact location and gradually move it back to where you want it at the rate of one foot per day
if there are several places, try putting dishes of cat food in those areas to discourage further elimination there
experiment with different textures of litter (cats prefer sandy litter)
use a covered litterbox for cats that stand in box but eliminate outside of it

Litter box problems

overcrowding: too many cats using same box
failure to change littter frequently enough -- some cats won't use a dirty box
failure to provide constant access to litterbox
change in type of litter used
change in location of litterbox
unfamiliar, frightening, or loud objects near box: dishwasher, etc.
food and water too close to litterbox
objectionable chemical used to wash or disinfect litterbox
location preference: your cat may want the box in a different location
texture preference: your cat doesn't like the feel of the litter
failure to cover litter: learned process from parents

use of litterbox is instinctive
cats that don't cover litter may be more prone to litterbox problems
your cat may be indicating texture preference problem

Psychological stress

most common manifestation is inappropriate urination

addition or subtraction of other pets in household visitors, company, parties, redecorating, construction, or any type of commotion a move to a new environment change in routine or schedule: a new job or working hours their return from boarding or hospitilization interaction problem with other pets or cats

cats are asocial rather than antisocial; in the wild each has a territory and period of contact with others in the group (and only one male per group)

a closed environment will create a greater degree of interaction than some cats prefer. The more cats in a household, the greater the degree of interaction

Treatment:
eliminate if possible
try to provide each cat at home with its own "space"

use favorite resting areas to determine
provide separate litterboxes near each space if possible
cubicles, boxes, shelves, crates are effective for this

tranquilizers sometimes work well in multicat situations

Chemical attraction of previous 'accidents'

likely to produce repeated visitations to the same spot

may induce urination by other members of a multi-cat household

you may have moved to a residence previously occupied with other dogs and/or cats

Treatment:
dispose of all soiled fabric or throw rugs if possible
50% vinegar or commercial products may be used
steam cleaning may help
repellants may help
do not replace carpeting until problem entirely solved or it may start all over again on your new carpeting

Treatment

Rule out medical problems FIRST
complete history and physical
stool/GI workup for diarrhea (if needed)
urinalysis for inappropriate urination to rule out an infection
workup for polydipsia/polyuria
important to check all cats of a multi-cat household

last cat seen misbehaving may be responding to chemical attraction and not be an instigator
more than one cat could have problem

treat/correct medical problems first. Behavioral problems can only be diagnosed in a healthy cat

Confinement

In portable kennel with litterbox, (with appropriate corrections) to stop further inappropriate behavior while medical and/or other problems are being treated.

particularly beneficial for transient stress induced problem
may allow acclimation to stress situation where source of stress cannot be eliminated
procedure

choose an area that can be a permanent location of litterbox
keep cat confined to this area 4-6 weeks when not under your direct visual supervision (if your cat attempts elimination outside of kennel when you are watching, squirt with water pistol as soon as elimination posture is attempted and put cat back in kennel)
if cat is using box regularly for 4 to 6 weeks when not under your gradually give access to larger and larger areas of your home, one room or hallway at a time

allow 1 week of good behavior in the new area before adding the new room
never increase access area until you are 100% certain cat's use of litterbox is 100%
if accident occurs, re-evaluate this material to make sure litterbox problem or something else didn't trigger

begin confinement over again and double intervals for relapses

For inappropriate urination problems in which all else fails and the alternative is euthanasia, hormone therapy may be attempted.

only for neutered cats only 50% effective
side effects may include increased appetite (common), depression or lethargy (less common). Long term use might have side effects such as: mammary enlargement, adrenocrotical suppression, and diabetes mellitus.
usually requires lifelong maintenance on regular intermittent basis
very dangerous drug; use borders malpractice -- should be reserved for cats who will be put to sleep if problem is not solved

immunosuppressive
weight gains predisposing to obesity
mammary gland development
feminization of males
may induce latent diabetes

dosage is initiated daily for 7 day trial; if effective, then dosage is tapered to least effective amount given every other day every one to two weeks
relapses may be expected when drug is discontinued