Itching and Associated Diseases

Itching or pruritus is defined as the skin sensation that prompts the patient to scratch a particular area of the skin. Irritative stimulation of skin is caused due to activation of free nerve endings situated at the dermo-epidermal junction. Itching is a physiologic or pathologic symptom caused due to internal or external factors. Itch receptors present in the free nerve endings at the dermo-epidermal junction are stimulated by histamine and other anaphylactic substances and evoke motor response of scratching. If not controlled, scratching may lead to skin injury and infection. There is a scratching itch cycle and one feels relieved after the itching cycle. Itching or pruritus is the most common disease of the skin caused by innumerable causes. If the cause of itching/pruritus remains undiagnosed even after two weeks then it is labeled as pruritus of undetermined origin (PUO). The cause of itching/pruritus could be local or systemic. It can be associated with the following systemic diseases.

Renal disease and pruritus:

Chronic renal failure (CRF) is a well-recognized cause of generalized and persistent pruritus. Uremia during CRF and cellular changes in the skin could be the possible cause of itching/pruritus. It is not directly related to renal function parameters, as patients with acute renal failure (ARF) do not complain of itching.

Liver disease and pruritus:

Patients with liver disease may also present with mild transient or severe or persistent sensation of itching. Intra-hepatic or extra-hepatic cholestasis in these patients leads to pruritus or itching. Primary billiary cirrhosis, cholangitis, viral infections, drugs and pregnancy can cause intra-hepatic cholestasis and lead pruritus.

Pregnancy and pruritus:

Pregnant women with mild abnormalities of liver function in the form of cholestasis may develop itching in the third trimester of pregnancy. Three out of 100 pregnant women may have pruritus.

Endocrine diseases and pruritus:

Pruritus confined to genital or peri-anal areas is most common in diabetics. Patients with diabetes mellitus sometimes may present with pruritus as the main presenting feature for medical consultation. Patients suffering from hypothyroidism and hyperthyroidism may also have generalized itching or pruritus.

Pruritus in occult malignancies:

Intense itching of nostrils has been observed in patients with tumors of brain. Adenocarcinomas and squamous cell carcinomas of various organs may also lead to generalized itching/pruritus. Around 30% patients with Hodgkin's disease have been found to be affected by itching disorder; some patients may show these symptoms as presenting features.