Dermatology 5th year, 2nd lecture (Dr. Mohammad Yousif)

It is the most common symptom of inflammatory skin diseases.

An essential characteristic of itch is that the only peripheral tissue from which it can be evoked is skin, with the single exception of cornea.,[object Object]

Pruritus Without primary skin lesions But with secondary skin lesions, e.g. ulcer, excoriations, lichenification, hyperpigmentation, etc. Generalized pruritus without 1ry skin lesions Manifestations of syst. dis. Generalized idiopathic pruritus

Causes of pruritus I) Pruritus from skin diseases These diseases often have characteristic lesions and locations. However, rubbing and scratching may conceal the primary lesions.

I) Pruritus from skin diseases (Cont’d) A) Severely pruritic dermatoses Scabies / phthirus pubis DH LP Urticaria Contact dermatitis Atopic dermatitis Drug eruptions PUPP of pregnancy Herpes gestationis Mycosis fungoides No scratch marks 10

I) Pruritus from skin diseases (Cont’d) B) Moderately pruritic dermatoses Seb. Dermatitis. Polymorphous light eruption. Urticaria pigmentosa. Fungal infections. Asteatotic eczema (xerosis): aggravated by low humidity during winter (winter itch). 5

Causes of pruritus (Cont’d) II) Exogenous causes of pruritus Sunburn. Chilblains. Aquagenic pruritus. Insect bites / animal mites. Detergents / fiberglass. 5

Causes of pruritus (Cont’d) III) Systemic causes of pruritus: Systemic causes of pruritus can be summarized by the mnemonic BLINKED.

III) Systemic causes of pruritus (BLINKED) (Cont’d) Blood disorders ,[object Object]

Polycythemia vera (50% of patients): classically, it follows a hot bath, with drop in temperature when the patient emerges from the bath, triggering the pruritus. It is pricking in nature and lasts 30-60 minutes.,[object Object]

HCV: in patients with pruritus, 4% may have HCV.,[object Object],[object Object]

Psychogenic pruritus, in contrast to organic pruritus, DOES NOT awaken patients from their sleep

III) Systemic causes of pruritus (BLINKED) (Cont’d) Neoplastic ,[object Object]

Multiple myeloma.,[object Object]

Psychogenic pruritus, either generalized or localized, e.g. psychogenic anogenital pruritus.,[object Object]

Hyperthryoidism (4-11% of patients).

Hypothyroidism (2ry to xerosis).

Carcinoid syndrome.,[object Object],[object Object]

Approaching the pruritic patient The approach to the patient with generalized pruritus without primary skin lesions is in the same manner as a patient with factitious dermatosis. Both are diagnoses of exclusion, i.e. all organic causes must be excluded within reasonable limits.

15 points should be discussed in the history

Approaching the pruritic patient 1. Is the itching localized or generalized? ,[object Object]

Duration of each attack.,[object Object]

Burning sensation.,[object Object]

Phthirus pubis (after single exposure, > 1/3 patients have another STDs).,[object Object]

Healthcare workers.,[object Object]

Approaching the pruritic patient 6. Have you been exposed to any animal? ,[object Object]

Approaching the pruritic patient 8. How do you bath? ,[object Object]

Hot water, harsh soap dryness dermatitis.

Bathing aquagenic itch.,[object Object],[object Object]

Approaching the pruritic patient 11. Have you started any new drugs in the past few months? ,[object Object],[object Object]

Psychogenic itching does not interfere with sleep.,[object Object]

Approaching the pruritic patient 14. Do you have a prior history of this type of itching? Is it recurrent? ,[object Object],[object Object]

Alleviation by cooling.,[object Object]

Enlargement of LN, spleen, liver  lymphoma.

Rectal examination and pelvic examination (female)  malignancy.

Oral candidiasis  LN++  HIV.

Examine for excoriations and lichenification.,[object Object]

Renal function tests: urea, creatinine.

Liver function tests: alkaline phosphatase (best screening test), bilirubin. Serum antimitochondrial antibody test is highly sensitive and specific for diagnosis of primary biliary cirrhosis (PBC).

Feces for: parasites, occult blood (> 40 years).

Fasting glucose.,[object Object]

Pathophysiology ,[object Object]

From there, the impulse is transmitted to the dorsal horn of the spinal column via unmyelinated C fibers and thin myelinated (A delta) fibers, across the midline and then in the lateral spinothalamic tract to the thalamus and finally to the sensory cortex.,[object Object]

Morphine relieves pain but can produce itching. Its antagonist “Naloxone” inhibits itch but lowers pain threshold.

Pruritic stimuli exert their action near or at the DEJ, while pain from deeper nerve endings in the skin.,[object Object]

Mediators of itching ,[object Object]

Dermatology 5th year, 2nd lecture (Dr. Mohammad Yousif)

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