Patricia Arrastía and María Gabriela Garrido

Itching or itching is a frequent reason for consultation in medical practice. Subjective in nature, it can be defined as a sensation that leads to scratching.

Sometimes it is the only symptom for which the patient consults or it may coexist with other symptoms and signs.

It is important to carry out an interrogation and a complete physical examination, as well as the corresponding complementary studies to arrive at the diagnosis, considering that it may be the predominant symptom of inflammatory skin diseases or it may be a manifestation of metabolic, neoplastic or drug processes.

Pathophysiology

The sensation of itching is the result of the activation of a network of nerve endings located at the dermoepidermal junction, considering that if the stimulus on said endings were of greater intensity it would produce pain.

Current evidence indicates that histamine and various peptides (bradykinin, interleukins, neuropeptides, substance P, kallikrein, CNS opioid peptides, among others) would be the chemical mediators of the itching process.

It is thought that it is transmitted by the unmyelinated C fibers, taking the stimulus to the posterior cord of the medulla, from there to the thalamus through the lateral spinothalamic tract to end in the posterior central gyrus of the cortex.

The scratching response to itching is a spinal reflex, which would calm it by producing a sensation of mild pain that overlaps the itching.

Types of itching

1. PRURITUS ASSOCIATED WITH DERMATOLOGICAL DISEASES:
   1. INFECTIOUS
      • Bacterial (impetigo, folliculitis)
      • Viral (herpes, chickenpox)
      • Mycosis (candidiasis, had capitis, had cruris)
      • Parasitic (scabies)
   2. ENVIRONMENTAL
      • Plastics
      • Fabrics
      • Poland
      • Sunburn
   3. SKIN DISEASES
      • Atopic eczema
      • Lichen planus
      • Seborrheic dermatitis
      • Psoriasis
      • Pityriasis rosea
      • Dermatitis herpetiforme
      • Mycosis fungoides
      • Ictiosis
   4. ALLERGIC REACTIONS
      • Contact dermatitis
      • Pharmacoderma
      • Urticarias
      • photoallergy
   5. XEROSIS
2. PRURITUS ASSOCIATED WITH SYSTEMIC DISEASES
   1. Liver disease: generalized pruritus may appear in pregnancy with elevated bilirubin values ​​due to cholestasis caused by estrogens. Pruritus in chronic biliary obstruction is associated with elevated levels of bile salts, but there is no direct relationship between these levels and the intensity of the symptom.
   2. Chronic kidney disease: it is one of the most frequent symptoms. The excessive dryness of the skin, added to the high levels of uremia would be responsible. Hemodialysis produces temporary relief.
   3. Pruritus in endocrine diseases: generalized pruritus is a symptom of thyrotoxicosis, and may be related to the increase in body temperature. In hypothyroidism, the presence of pruritus is possible due to the intense dryness of the myxedema skin. In both cases, it may be located mainly in the genital area due to mucocutaneous candidiasis. In hyperparathyroidism, pruritus could be related to elevated calcium levels, while parathormone stimulates mast cells, increasing histamine production. In diabetes, generalized itching is rare, but localized it is, predominantly in the genital area, due to the increased incidence of cutaneous candidiasis.
   4. Pruritus in malignant diseases: Hodgkin's disease presents generalized pruritus in 30% of cases. 50% of patients with polycythemia vera associate intense water-induced itching. Other diseases such as multiple myeloma, neoplasms of the pancreas, ovaries, stomach and prostate can be accompanied by itching.
   5. Psychiatric diseases: Parasitophobia, in which the patient reports tingling, is a symptom of a severe psychoneurotic disorder. More frequently, localized or generalized itching can be a manifestation of anxiety or depression. In general, the diagnosis is made by exclusion.

Study methodology

• Full questioning
• Physical Exam, look for the presence of skin lesions, signs of scratching, skin color, state of hydration, presence of lymphadenopathy or visceromegaly, etc.
• Complementary tests: blood laboratory, microbiological studies, skin biopsy, etc.