Cryosurgery for warts in general practice

Cryosurgery for warts in
general practice
Dermatology
Patient selection and technique are key factors in successful cryosurgery
treatment for warts in general practice, writes David Buckley
Picture 3. Periungual warts –
before cryosurgery
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Picture 4. Periungual warts – one
month after cryosurgery
Picture 5. Periungual
warts – two months after
cryosurgery
Picture 1 & 2. Hand wart before and after three sessions of cryotherapy
Cryosurgery is a method of selectively destroying
unwanted tissue using cold liquids or gases. The aim
is to cause maximum tissue destruction in the target
lesion with minimal collateral damage to the surrounding healthy structures. Cryosurgery does not kill the wart
virus; in fact viruses can survive and be preserved in
liquid nitrogen. What we are trying to do with cryosurgery
is to destroy the cells that are infected with the wart virus
by creating intracellular ice crystal formation that ruptures the cell, thus allowing clean, healthy, uninfected
cells to take their place.
Post-cryosurgery there is a lot of swelling which blocks
the small feeding vessels causing ischaemic necrosis to the
frozen area, enhancing cell death. In addition, cryosurgery
has the unique action of ‘cryoimmune stimulation’, whereby
some of the wart virus is released from the frozen wart after
cryosurgery, presenting wart antigen to the immune system.
This acts like a vaccine, helping the body to fight off the
human papillomavirus (HPV) in the treated and sometimes even distant untreated warts. Patients who have a
suppressed immune system are less likely to benefit from
‘cryoimmune stimulation’. Combining imiquimod (Aldara)
with cryosurgery may enhance this response.1
There is only one important rule in cryosurgery: never
freeze any lesion unless you are 100% sure of the diagnosis. If you cannot make a confident named clinical
diagnosis, do not freeze – take a biopsy or refer the patient
for another opinion.
Success in cryosurgery is dependent of four main factors:
cryogen, delivery system, patient selection and technique.
Table 1: Types of cryogens
Ice (water)
-5°C
Ice (saturate salt and water mix)
-25°C
Dimethyl ether and propane in a bud
-32°C
Nitrous oxide
-89°C
Liquid nitrogen
-195°C
Cryogen
Maximum cell destruction is achieved by a rapid freeze,
achieving temperatures of less than -40°C at the base of
the lesion, a slow thaw and carrying out at least two freeze
thaw cycles.2 This can generally only be achieved by using
liquid nitrogen which is the coldest (-196°C), most versatile, cheapest cryogen available (see Table 1).
Over the counter cryogens such as home freezers like
Wartner, which contain a mixture of dimethyl ether and
propane (DMEP), are much less effective, as most only get
down to -32°C at the surface of the wart with a very slow
freeze. Hand held medical devices such as Histofreezer or
Dermafreeze also contain DMEP and are equally ineffective
and far too expensive per unit cost to make them practical
in general practice. Nitrous oxide gas, while not as cold
as liquid nitrogen, can reach -89°C and can give reasonably good results provided there is meticulous attention to
technique.
Liquid nitrogen cryosurgery via a closed hand held cryogun is the safest, most effective, most versatile method to
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Dermatology
deliver a freeze. Applying liquid nitrogen with cotton bud is
not as affective but is still more effective than nitrous oxide
gas or Histofreezer.
Patient selection
Patient selection is crucial in delivering effective cryosurgery. Children under the age of six do not make good
candidates for cryosurgery for warts and doctors should
resist parental pressure to freeze warts in this age group.
The only exception is freezing molluscum contagiosum,
which usually clear up with a tiny, almost painless, three
second freeze.
Children between the ages of six and 12 years are generally poor candidates for cryosurgery unless the child (not
just the parent) is highly motivated, can understand what
is involved and is very eager for treatment. I will not treat
children with cryosurgery for warts greater than 4-5mm in
diameter or a cluster of warts together, unless the child can
tolerate local anaesthetic.
Other poor candidates for cryosurgery are needle phobics
and patients with immune suppression such as diabetes or
transplant patients.
Technique
There is a limit to the depth of freeze one can achieve
with cryosurgery. As you freeze from the surface down,
the isobars get progressively warmer until equilibrium is
reached between the cold of the cryogen at the surface and
the heat of the skin from the underlying circulation (see
Table 2). Hypertrophic warts are often covered with thick
keratin, which acts as a thermal insulator. This has to be
removed with a blade to allow the freeze to penetrate to the
base of the wart. Even after removing keratin, many large
warts can be 4-5mm deep.
Success with cryosurgery is increased dramatically when
a wart is debulked. Generally, this can only be achieved
by applying local anaesthetic and surgically paring down
the wart. For hand warts, I like to have them flush with the
surrounding skin before beginning cryosurgery. For plantar
warts, I usually pare them out leaving a crater to freeze into.
In this way, I aim to remove 75-90% of the wart before
starting the freeze. Another bonus is that the local anaesthetic makes the whole procedure far more tolerable for
patients and more enjoyable for the doctor.
For most warts greater than 4-5mm in diameter or for a
cluster of warts together, the discomfort of a prick with a
30 gauge needle with local anaesthetic is generally a lot
less painful than trying to treat the wart using cryosurgery
without local anaesthetic.
Using this technique, I constantly get a success rate of
over 90% with a single treatment for hand warts and verrucas3 (see Picture 1 & 2). Another advantage to debulking is
that there is less necrotic tissue to die off post-cryosurgery.
The only disadvantage is that there can be a lot of bleeding
during and after the treatment. You have to be careful not
to contaminate your cryogun with blood. I put on a fresh
glove just before I pick up my cryogun for the freeze. Postoperative bleeding can usually be controlled with a pressure
dressing and elevation. Post-operative pain can usually be
controlled by giving paracetamol or ibuprofen immediately
after the session of cryosurgery, before the local aesthetic
has had time to wear off. Most warts will heal in three to
six weeks.
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Table 2: Development of thermal
gradients within evolving cryolesion
Liquid N2
cryogen heat sink
A
B2
C2
B2
C2
B
C
in vivo skin
Temperature of ice front: A = -120°C; B = -50°C; C = -25°C
Temperature of ice zones: B1 & B2 = -30°C; C1 & C2 = -5°C
Table 3: Freeze-thaw cycles
Type of wart
Freeze times
(seconds)
Freeze-thaw
cycles
Molluscum contagiosum
3
1
Periungual wart
7
1
Filiform wart
10
1
Ano-genital wart
10
1-2
Common wart
10
2
10-15
2
15
2
Plantar wart
Mosaic plantar wart
Most bulky warts require two freeze-thaw cycles (see
Table 3). There is some controversy, even among expert
cryosurgeons, about what constitutes a freeze-thaw cycle.
However, most now agree on the following definition:
Freeze-thaw cycle
• Start freezing as quickly as possible until the whole wart
is frozen
• Continue freezing until a halo of normal uninfected skin,
1-2mm around the wart, is also frozen
• Continue to freeze (at a slower rate to avoid excessive
lateral spread) for 10 seconds
• Then let the wart thaw out completely without heating,
before starting a second freeze-thaw cycle in exactly the
same way, if required.
Freezing down the auroscope cone is a useful technique
for plantar warts, which allows you to get deep penetration
of the freeze, without too much lateral spread. This leads to
a higher success rate with lower morbidity, such as blisters.
Spray down the auroscope cone with a C or E spray tip for
10 seconds only, as this is a much more concentrated form
of cryosurgery than using the open spray technique.
Flat warts (plain warts) are usually quite superficial and
so are much easier to treat. They do not usually require
paring or debulking because they are usually small and
can often be treated without local anaesthetic. Ano-genital
and mucous membrane warts are usually soft with no keratin and again do not usually require paring or debulking
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Table 4: Side effects of cryosurgery
Immediate
Pain
Swelling
Delayed
Blister formation – serous or
haemorrhagic
Ulceration
Secondary Infection
Prolonged
Hypopigmentation
Hyperpigmentation
Contracted scar
Hypertrophic scar
Paraesthesia
Skin atrophy
Hair follicle loss
before cryosurgery. Amitop (tetracaine) topical anaesthetic
works well and quickly (about 15 minutes) on mucous
membranes.
Periungual warts usually occur as a result of damage to
the cuticle, which is normally self inflicted from biting or
picking (see Picture 3).They can be difficult to manage,
as the periungual skin is very delicate. I usually pare them
down and freeze them gently with a five to seven second
freeze and only one freeze-thaw cycle.
Side effects
Pigmented changes (hypopigmentation or hyperpigmentation) can sometimes occur, particularly in dark
skinned patients, but the pigment usually comes back
after a few months, particularly when the freeze-thaw
cycle is not more than 10 seconds (see Table 3). Nerve
damage is very rare when treating warts. If it does occur,
for instance on the digital nerve, it may result in a temporary numbness of the side of the finger that will resolve
after a few months.
Success rate
The maximum number of warts I would treat in any one
session is approximately six to 10. The maximum number
of times I would freeze any one wart is three different
sessions. If they are not cleared after this, there is little
point in persisting with cryosurgery. I would usually then
revert to other techniques or perhaps try and encourage
the patient to simply live with the wart and keep it under
control by paring it at home, which makes it look and feel
better.
David Buckley is in practice in Tralee, Co Kerry
Treatment of warts and other skin surgical procedures will be discussed
at the second annual scientific meeting of the Primary Care Surgical
Association which takes place in Galway on April 19-20. For a programme
and registration form, email David Buckley at: info@asctralee.com
References
1. Gaitanis G et al. Immunocryosurgery for basal cell carcinoma; results of a
pilot, prospective, open-label study of cryosurgery during continued imiquimod application. J Eur Acad Dermatol Venerol 2009; 23:1427-1431
2. Baust JG et al. The patho-physiology of thermoablation:optimizing cryoablation, Curr Opin Urol 2009; (19) 127-132
3. Buckley D. Cryosurgery treatment of plantar warts. Ir Med J 2000, 93(5):
140-143
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