11.2 Pruritus in palliative medicine Flashcards
Afferent itch neurons synapse in what part of the spinal cord? Which spinal cord tract do itch neurons travel in? What is the reflex response to itch? Why type of neurons carry itch signals?
The C fibres terminate in substantia gelatinosa in the dorsal horn of the spinal cord
Lateral spinothalamic tract relay axons (spinothalamic lamina I neurons) cross and ascend contralaterally at the spinal level of entering sensory neurons
Itch neurons are specific type C fibres in skin, each having a wide innervation territory, thin axon, and very low conduction velocity
Aversive motor response is reflex
Give two examples of physical stimuli that can trigger itch. Give two examples of chemical stimuli that can trigger itch. What is the best characterized pruritogenic peptide?
Physical stimuli - pressure, thermal stimulation, low intensity electrical stimulation, formation of suction blisters, epicutaneous application of caustic substances
chemical stimuli - histamine, proteases, prostaglandins, and neuropeptides, also proteases such as trypsin, chymotrypsin, papain, and kallikrein
Substance P is best characterized pruritogenic peptide
List three mechanisms for how opioids can trigger pruritus
At the peripheral level within skin, opioids stimulate mast cell degranulation and release of histamine which produces itch
opioids stimulate an inhibitory presynaptic signal transmitted to primary afferents that modulates secondary transmission of itch.
opioids may induce itching by blocking the painful stimuli that suppress activity of central itch neurons.
According to the international forum for the study of itch, what are four categories of itch etiology?
dermatologic
systemic
neurogenic
psychogenic
Give four examples of exogenous dermatologic causes of pruritus and 4 examples of endogenous dermatologic causes of pruritus
Exogenous - scabies, insect bites, folliculitis, and allergic contact dermatitis, sunburn
Endogenous - atopic dermatitis, bullous pemphigoid, lichen planus, psoriasis, and urticaria
List five categories of systemic disorders associated with pruritus (box 11.2.2); given an example of each
Biliary and hepatic disease:
Biliary atresia
Primary biliary cirrhosis
Sclerosing cholangitis
Extrahepatic biliary obstruction
Cholestasis of pregnancy
Drug-induced cholestasis
Chronic renal failure—uraemia
Drugs:
Opioids
Amphetamines
Cocaine
Acetylsalicylic acid
Quinidine
Niacinamide
Etretinate, Acitretin
Other medications
Subclinical drug sensitivity
Endocrine diseases:
Diabetes insipidus
Diabetes mellitus
Parathyroid disease
Thyroid disease (hypothyroidism, thyrotoxicosis)
Haematopoietic diseases:
Hodgkin’s and non-Hodgkin’s lymphoma
Cutaneous T-cell lymphoma (mycosis fungoides, Sézary’s
syndrome)
Systemic mastocytosis
Multiple myeloma
Polycythaemia vera
Iron-deficiency anaemia
Infectious diseases:
Syphilis
Parasitic
HIV
Fungal
Malignancy:
Breast, stomach, lung, etc.
Carcinoid syndrome
Neurological disorders:
Distal small-fibre neuropathy
Stroke
Multiple sclerosis
Tabes dorsalis
Brain abscess/tumours
Psychosis, psychogenic causes
Delusions of infestation (parasitosis)
List four topical agents that can be used to manage pruritus
Phenol - anaesthetizes cutaneous nerve endings
mentol-camphor -counter-irritant and anaesthetic properties
Zinc oxide, coal tars, calamine, glycerine, and salicylates
Pramoxine hydrochloride is a topical anaesthetic
EMLA/topical local anesthetic cream or patches
Combinations of amitriptyline (1–2%) and ketamine (0.5–5%)
doxepin
capsaicin
List the four drugs recommended for the management of cholestatic pruritus according to the AASLD
cholestyramine
rifampicin
naloxone
sertraline
List five classes of drugs that can be used to systemically treat pruritus and give an example from each class
Anti-inflammatory agents
Corticosteroids
H1, H2, H3 blocking agents
Salicylates
Cromolyn
Thalidomide
Vasoactive drugs
α-blockers
β-blockers (e.g. propranolol)
Central and peripheral nervous system agents
Anaesthetic agents:
Lidocaine - use do infusion for refractory prurtius
Propofol
Ketamine
Antidepressant agents - TCAs- doxepin, amitriptyline, nortriptyline (have antihistamine effects), SSRIs - paroxetine
Neuroleptic agents - pimozide, haldol
Tranquillizing agents
Sedatives - diazepam
Opioid antagonists (naloxone, naltrexone, nalmephene)
Serotonin antagonists (ondansetron)
Analgesic (non-conventional, voltage-gated calcium channel)
Neurokinin receptor antagonist agents:
Aprepitant
GABA agonists-voltage-gated calcium channel modulators:
Gabapentin
Pregabalin
Sequestrants:
Cholestyramine
Charcoal
Heparin (IV)
List five pieces of advice to protect the skin in the setting of symptomatic pruritus
close trimming and filing of sharp edges of fingernails as well as wearing cotton gloves
tepid baths (a hot bath feels more relaxing and offers symptom relief, but the itch is worse afterwards due in part to vasodilation and the accentuated neural response of cutaneous heating)
lubricate the skin with a fragrance-free, cream-base emollient containing phenol or menthol if this is found to be beneficial
Wearing clothing that is loose fitting, less irritating (e.g. avoid wools), and minimizes heat retention and sweating
Provide two examples of situations where antihistamines are not beneficial for pruritus
Hodgkins disease
obstructive jaundice
uremic pruritus
List four chemical mediators of temperature regulation
catecholamines
acetylcholine
eicosanoid prostaglandin E,
Hypothalamic peptides (thyrotropin-releasing hormone, bombesin, neurotensin, adrenocorticotropic hormone, and vasopressin)
List four triggers for thermal stimulation of eccrine sweat glands. Where on the body does thermal stimulation trigger sweating? What NT is responsible for sweat gland activation?
Triggers - body position, exercise, dehydration, sweat gland blood flow, ambient humidity, gender, and age
Thermal sweating - uniform sweat response over the body surface while sparing the palms and soles
Eccrine glands are innervated by cholinergic fibres -> acetylcholine
What type of stimulation triggers sweating in the palms and soles? What two brain structures control this?
Mental sweating
The palms and soles show a baseline sweat pattern in the waking state, and mental excitement and stress will increase the rate.
Mental sweating is controlled by the cerebral neocortex limbic system and hypothalamus.
Give two etiologies of localized hyperhidrosis
Essential (primary)
Neurogenic:
Spinal cord disease
Peripheral neuropathy
Cerebrovascular disease (stroke)
Intrathoracic neoplasms or masses
Unilateral circumscribed
Cold-induced
Associated with cutaneous lesions
Gustatory
