The kidney and its skin expressions

Chronic renal failure (CRF) is a recognized significant problem in many parts of the world, including the Philippines.  It refers to an irreversible deterioration in renal function, which classically develops over a period of years.  The disorder has five stages.  Each stage is a progression through an abnormally low and deteriorating glomerular (a part of the kidney that serves to filter toxic or unwanted substances) filtration rate which is usually determined indirectly by the serum creatinine level   All individuals with either kidney damage or a glomerular filtration rate (GFR) <60 ml/min/1.73 m² for three months are classified as having CRF.  Stage five is the last stage in CRF and is called the end-stage renal failure (ESRD), a severe illness that requires some form of renal replacement therapy (dialysis or kidney transplant).  Hemodialysis is one of the therapeutic modalities which can improve the quality of life in these patients without having to undergo surgery.  Fifty-percent of patients with ESRD have at least one associated cutaneous change.  Cutaneous findings can precede or follow the initiation of hemodialysis treatment and chances of developing newer skin with this therapeutic modality increase as it increases the life expectancy of CRF patients.  Both CRF and hemodialysis therefore are associated with abnormal changes, including those of the mucous membrane, skin, hair, and nails in these patients.

• Xerosis. Most common. Intensity varies from mild to severe, predominantly seen on the extensor surfaces of the forearms, legs, and thighs. 

• Pruritus. May be episodic or constant, localized or generalized, and mild to severe in intensity.  When localized, the forearms and upper back are predominantly affected.  Cutaneous manifestations of pruritus include excoriations, prurigo nodularis and lichen simplex chronicus.  Exact cause is unknown but is thought to be associated with uremia.  Slowly accumulated or deposited pruritogens of as yet uncertain nature are also the likely cause.  It has also been associated with the degree of renal insufficiency (urine output of <500 ml), secondary hyperparathyroidism, xerosis, increased serum levels of magnesium, calcium, aluminum, phosphate, and histamine (due to allergic sensitization to various dialyzer membrane components). 

Pigmentary changes are of two types: Brownish black due to retention of chromogens and deposition of melanin in the basal layer and superficial dermis (failure of kidneys to excrete beta melanocyte- stimulating hormone ) and the yellowish color (occurs in 40%) attributed to the accumulation of carotenoids and nitrogenous pigments (urochromes) in the skin.

• Pallor. This can be caused by anemia.

• Purpura and Ecchymosis. Easy bruising occurs in 20% of CRF patients not on dialysis. 

• Uremic frost. Patients in pre-dialysis era who exhibit uremic frost have a blood urea nitrogen level of more than 250-300 mg/dl. 

• Calcification and calciphylaxis. These are a rare phenomena in uremic patients.  An abnormally elevated level of parathyroid hormone (PTH) may trigger the deposition of crystalline calcium pyrophosphate in the dermis, subcutaneous fat or arterial walls.  Occasionally, a syndrome called calciphylaxis has been reported in CRF patients due to acute thrombosis of calcified vessels producing violaceous skin mottling that’s acutely painful due to ischemia (leading to necrosis and gangrene), a condition associated with high mortality  

• Cancerous and precancerous lesions.

• Delayed wound healing.

• Nail changes. Increased nail pigmentation, usually a brownish discoloration that does not fade on pressure, combined with a proximal white zone that gives rise to half-and-half nails.  More prevalent in diabetics.  Fungal nail infections are also common. 

• Hair changes. Hair loss most common and associated with severity of illness or due to drugs (heparin, anti-hypertensive, lipid-lowering) used in these patients, sparse body hair, discoloration, and dryness of hair.  Dry and lusterless hair is due to a decrease in the secretion of sebum.  Hair changes occur in 10 to 30% CRF patients not on dialysis.

A clinician should be highly vigilant while examining patients with these dermatologic changes.  These dermatologic findings may even precede any clinical or biochemical evidence in CRF patients.  The early recognition and treatment of cutaneous signs can relieve suffering and decrease morbidity of these patients.

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