Etiology/Pathophysiology
Cytotoxic Chemotherapy
Radiation Therapy
Combination Therapy
Biologic Response Modifiers
Bone Marrow Transplantation
Other Pharmacologic Support During Cancer Treatment
Infection
Hematologic disorders that cause pruritus include polycythemia vera. Some
conditions that cause iron deficiency, including exfoliative skin disorder,
also cause pruritus. Diabetes and thyrotoxicosis are endocrine causes of
pruritus.[1]
Pruritus is a frequent clinical manifestation of people with AIDS, AIDS-related
Kaposi sarcoma, and AIDS-related opportunistic infections. Pruritus with or
without rash has been reported in approximately 84% of people with AIDS and
35.5% of those with AIDS-related Kaposi sarcoma. The incidence of pruritus
associated with AIDS-related opportunistic infections approaches 100%.[2]
Various malignant diseases are known to produce pruritus. Hodgkin lymphoma
causes pruritus in 10% to 25% of patients. In some instances, pruritus
precedes diagnosis of the lymphoma [1] and may be an indicator of a less
favorable prognosis when associated with significant fever or weight loss (“B”
symptoms).[3] Pruritus associated with Hodgkin lymphoma is characterized by
symptoms of burning and intense itching occurring on a localized skin area,
frequently on the lower legs. Other lymphomas and leukemias have been
associated with a less intense but more generalized pruritus. Adenocarcinomas
and squamous cell carcinomas of various organs (i.e., stomach, pancreas, lung,
colon, brain, breast, and prostate) sometimes produce generalized pruritus that
is more pronounced on the legs, upper trunk, and extensor surfaces of the upper
extremities.[1,3] Pruritus associated with malignant diseases has been
observed to diminish or disappear with eradication of the tumor and reappear
with recurrence of disease.[3]
Drugs associated with secondary pruritus include opium derivatives (cocaine,
morphine, butorphanol), phenothiazines, tolbutamide, erythromycin estolate,
anabolic hormones, estrogens, progestins, testosterone and subsequent
cholestasis, aspirin, quinidine and other antimalarials, biologics such as
monoclonal antibodies, and vitamin B complex. Subclinical sensitivity to any
drug may be related to pruritus.[3]
Hypothesized mechanisms of pruritus have been inferred from studies of pain,
since pain and itching share common molecular and neurophysiological
mechanisms.[4] Both itch and pain sensations result from the activation of a
network of free nerve endings at the dermal-epidermal junction. Activation may
be the result of internal or external thermal, mechanical, chemical, or
electrical stimulation. The cutaneous nerve stimulation is activated or
mediated by several substances including histamine, vasoactive peptides,
enkephalins, substance P (a tachykinin that affects smooth muscle), and
prostaglandins. It is believed that nonanatomic factors (such as psychological
stress, tolerance, presence and intensity of other sensations and/or
distractions) determine itch sensitivity in different regions of the body.
The itch impulse is transmitted along the same neural pathway as pain impulses,
i.e., traveling from peripheral nerves to the dorsal horn of the spinal cord,
across the cord via the anterior commissure, and ascending along the
spinothalamic tract to the laminar nuclei of the contralateral thalamus.
Thalamocortical tracts of tertiary neurons are believed to relay the impulse
through the integrating reticular activating system of the thalamus to several
areas of the cerebral cortex. Factors that are believed to enhance the
sensation of itch include dryness of the epidermis and dermis, anoxia of
tissues, dilation of the capillaries, irritating stimuli, and psychological
responses.[1,3-5]
The motor response of scratching follows the perception of itch. Scratching is
modulated at the corticothalamic center and is a spinal reflex. After
scratching, itching may be relieved for 15 to 25 minutes. The mechanism
through which the itch is relieved by scratching is unknown. It is
hypothesized that scratching generates sensory impulses that break circuits
in the relay areas of the spinal cord. Scratching may actually enhance the
sensation of itching, creating a characteristic itch-scratch-itch cycle. Other
physical stimuli such as vibration, heat, cold, and ultraviolet radiation
diminish itching and increase the release of proteolytic enzymes, potentially
eliciting the itch-scratch-itch cycle.
A pinprick near or in the same dermatome as an itchy point will abolish the
itch sensation.[3] It is known that hard scratching may substitute pain for
the itch, and in some instances, the patient might find pain the more tolerable
sensation. It is thought that spinal modulation of afferent stimuli (Gate
theory) and central mechanisms may play a role in the relief of itch.[3]
Hypothesized pathogenesis of pruritus associated with underlying disease states
are varied. Biliary, hepatic, renal, and malignant diseases are thought to
produce pruritus through circulating toxic substances. Histamine released from
circulating basophils and the release of leukopeptidase from white blood cells
may trigger pruritus associated with lymphomas and leukemias. Elevated blood
levels of kininogen in Hodgkin lymphoma, release of histamine or bradykinin
precursors from solid tumors, and release of serotonin in carcinoid may all be
related to pruritus.[1,6]
People receiving cytotoxic chemotherapy, irradiation, and/or biologic response
modifiers for treatment of malignancy are likely to experience pruritus. This
same population is quite likely to be exposed to many of the other etiologic
factors relating to pruritus ranging from nutritionally related xerosis (dry
skin) to radiation desquamation, chemotherapy and biologic agent–induced side
effects, antibiotic reactions, and other drug sensitivities.
Cytotoxic Chemotherapy
Each of the major classes of antineoplastic agents (alkylating agents,
antimetabolites, antibiotics, plant alkaloids, nitrosoureas, and enzymes)
include drugs capable of producing cutaneous reactions including pruritus.
Patients receiving antineoplastic drugs frequently report dry skin and scaling,
thought to be related to effects on sebaceous and sweat glands.[7,8] Many
problems are self-limiting and require no active intervention. Other problems
warrant anticipation and implementation of preventive measures.
Hypersensitivity to cytotoxic agents can be manifested by pruritus, edema,
urticaria, and erythema. Hypersensitivity reactions vary in symptomatology and
depend on the drug, the dosage, and the allergy history of the patient. The
agents most associated with hypersensitivities include doxorubicin,
daunorubicin, cytarabine, L-asparaginase, paclitaxel, and cisplatin. In most
reports, these reactions have been localized to the area of the vascular access
and dissipate within 30 to 90 minutes.[9,10] More dramatic and even
life-threatening reactions can occur, and the development of pruritus may
represent an early stage of serious hypersensitivity reactions.[11]
Radiation Therapy
Radiation therapy–related pruritus is usually associated with dry desquamation
of skin within the treatment field. Dryness and pruritus may occur at an
accumulated dose of 20 Gy to 28 Gy,[12] and is caused by obliteration of
sebaceous glands within the field. This is an acute phenomenon that correlates
with the depletion of actively proliferating basal cells in the epidermal layer
of the skin, a fixed percentage of which die with each dose fraction of
irradiation. Remaining basal cells undergo cornification and shed at an
increased rate, while nonproliferating basal cells are stimulated and their
cell cycle shortened. Subsequent peeling of the skin is defined as dry
desquamation. The skin becomes dry, and the patient may notice itching and
burning sensations.[12] Dry skin is susceptible to further injury through
scratching and/or formation of fissures, augmenting the risk of infection and
tissue necrosis.
If the desquamation process continues, the dermis will eventually be exposed, resulting in moist desquamation. This side effect increases the risk of
infection, discomfort, and pain, possibly necessitating interruption of a
treatment plan to allow for healing. This interruption can compromise the final outcome of
cancer therapy. For this reason, it is desirable to anticipate and prevent the
progression of skin reactions to this stage.[13]
External beam therapy with electrons may elicit more skin reactions than photon
therapy since the depth of penetration and linear energy transfer is closer to
the skin surface with electrons. Radiation delivery techniques (bolus doses
and tangential fields) also influence the degree of reaction. Fields that
include skin folds (i.e., the axilla, breast, perineum, and gluteus) are
anticipated to have increased reactions because of friction, higher moisture
content, and low aeration.[14,15]
Combination Therapy
Therapy combining radiation and chemotherapy plays a significant role in
state-of-the-art cancer therapy. The synergism of these cytotoxic modalities
enhances normal tissue reaction and can be expected to precipitate higher
complication rates.[7] The total combined effects of the drugs and irradiation
exceed the individual effects of either modality. Significant cutaneous
reactions are thought to occur more frequently when chemotherapy and
irradiation are administered concurrently.[16]
Biologic Response Modifiers
Biologic response modifiers used in the treatment of malignant disease are
associated with a wide variety of side effects and toxic effects. Pruritus has
been a side effect associated with several biologics but has been most
reported in patients receiving interferons.[17-20] Reports of
pruritus as a side effect of biologics are primarily anecdotal and have not
been a focus of attention.
Bone Marrow Transplantation
Graft-versus-host disease (GVHD) affects 25% to 50% of patients who live longer
than 100 days after bone marrow transplantation. The incidence of skin GVHD is
reported to be 80% to 90%, and symptoms vary in severity and type.[21] Reported
skin changes include dryness and pruritic, erythematous, maculopapular rashes.
Onset can be subtle or sudden; skin GVHD can progress to scleroderma and
contracture.[22]
Other Pharmacologic Support During Cancer Treatment
Many pharmacologic agents employed at any point during the cancer course,
whether in a primary treatment plan or incorporated into a symptom control or
supportive care program, are capable of eliciting a pruritic reaction. These
drugs include morphine, other opium derivatives, and aspirin used in pain
management; corticosteroids; antibiotics; phenothiazines; and, to a lesser
degree, hormonal agents (estrogen, progestins, and testosterone).[3]
Mechanisms of these reactions range from hypersensitivity to chemical
interference with neural pathways.[4]
Infection
Pruritus can be a symptom of infection. Pruritus involving anal or vulvar
areas might be caused by infections with Trichomonas or fungi, local tumors,
hemorrhoids, anal fissures, fistula discharge, wound effluent, or surgical
wound drainage.
References
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