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Why can tuberculoid leprosy cause claw hand and foot deformities?

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Sign reading Gandhiji Prem Nivas Leprosy Centre Titagarh conducted by Missionaries of Charity, with a crucifix above the sign on a decorated building facade. — leprosy The Gandhiji Prem Nivas is a center for people with leprosy that was established by Mother Teresa in 1958 and is run by the Missionaries of Charity in Titagarh, India.

In tuberculoid leprosy, claw hand and foot deformities occur because of the body’s intense immune response to the leprosy bacillus. This reaction involves the formation of hard nodules, or tubercles, in the skin and deep tissues, which eventually spreads into the main trunks of peripheral nerves.1

As the cellular reaction infiltrates these nerves, it prevents the transmission of nerve impulses. This disruption leads to a loss of sensation and decreased circulation in the affected areas, most commonly the forearm or lower leg. The resulting nerve damage and loss of motor function cause the muscles to become paralyzed or inactive, which eventually leads to the characteristic clawing of the hand and gross deformities of the foot. Because patients lose the ability to feel pain, minor injuries often go unnoticed, leading to further tissue damage, eroding ulcers, and potential loss of fingers or toes.1