An extreme darkening of the skin has been reported by doctors in a dark-skinned Trinidadian, who is a resident of the Caribbean Sea off the northeastern coast of South America.

In a new study, published in the Journal of Medicine, doctors from the University of the West Indies in Trinidad and Toba described an unusual case of excessive darkening of the skin in a black man. 

A 59-year-old man came to the endocrinology clinic complaining of weariness for two months and increasingly darkening skin on his hands and soles for one year.

He worked as a tile layer and had attributed his symptoms to work-related hazards at first.

His tongue was smooth, with scattered patches of mucosal discoloration on physical examination (Panel A).

Hyperpigmentation was also present on the palms (Panel B) and soles.

Blood tests revealed mild leukopenia and thrombocytopenia, as well as a hemoglobin level of 9.4 g per deciliter (reference range, 14 to 18), a mean corpuscular volume of 117 fl (reference range, 80 to 94), and a mean corpuscular volume of 117 fl (reference range, 80 to 94).

Vitamin B12 concentration was 40 pg per milliliter (30 pmol per liter; reference range, 200–1100 pg per milliliter [150–810 pmol per liter]), and serum intrinsic factor antibody concentration was greater than 200 reference units per milliliter (reference value, 18), consistent with a diagnosis of vitamin B12 deficiency secondary to autoimmune gastritis.

Skin hyperpigmentation develops as a result of increased melanin synthesis in those who are deficient in vitamin B12, and it is more common in people who have darker skin.

With treatment, hyperpigmentation usually fades.

The patient was treated with parenteral vitamin B12, and at 4 months after presentation, the hyperpigmentation and exhaustion were disappeared (Panels C and D).

Anemia occurs due to a decrease in hemoglobin in erythrocytes and is usually manifested by symptoms of tissue hypoxia.

The symptoms of anemia are as follows:

• weakness,
• rapid fatigue,
• shortness of breath and headache.

Also, depending on the causes of anemia, it may be accompanied by additional symptoms:

• jaundice (destruction of erythrocytes or impaired sensitivity of nerve fibers in vitamin B12 deficiency),
• darkening of the skin and mucous membranes (in pernicious anemia – vitamin B12 deficiency – due to increased melanin synthesis in melanocytes).

The exact mechanism of hyperpigmentation is unknown, and it occurs in only 10% of patients, so doctors often miss this symptom.

Discoloration of the skin and mucous membranes often indicates a problem with the body. For example, American women have blue tongue due to antibodies to an enzyme involved in the synthesis of adrenal hormones. The change in color was reversible, but the woman will have to take hormone replacement therapy for life.

Source: 10.1056/NEJMicm2113099

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