Leprosy

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Leprosy, also called Hansen disease, is a disorder known since ancient times. It is caused by bacteria called Mycobacterium leprae and is contagious, which means that it can be passed from person to person. It is usually contracted by breathing airborne droplets from affected individuals' coughs and sneezes, or by coming into contact with their nasal fluids. However, it is not highly transmissible, and approximately 95 percent of individuals who are exposed to Mycobacterium leprae never develop leprosy. The infection can be contracted at any age, and signs and symptoms can take anywhere from several months to 20 years to appear.

Leprosy affects the skin and the peripheral nerves, which connect the brain and spinal cord to muscles and to sensory cells that detect sensations such as touch, pain, and heat. Most affected individuals have areas of skin damage (cutaneous lesions) and problems with nerve function (peripheral neuropathy); however, the severity and extent of the problems vary widely. Leprosy occurs on a spectrum, in which the most severe form is called multibacillary or lepromatous, and the least severe form is called paucibacillary or tuberculoid. Patterns of signs and symptoms intermediate between these forms are sometimes called borderline forms.

Multibacillary leprosy usually involves a large number of cutaneous lesions, including both surface damage and lumps under the skin (nodules). The moist tissues that line body openings such as the eyelids and the inside of the nose and mouth (mucous membranes) can also be affected, which can lead to vision loss, destruction of nasal tissue, or impaired speech. Some affected individuals have damage to internal organs and tissues. The nerve damage that occurs in multibacillary leprosy often results in a lack of sensation in the hands and feet. Repeated injuries that go unnoticed and untreated because of this lack of sensation can lead to reabsorption of affected fingers or toes by the body, resulting in the shortening or loss of these digits.

Paucibacillary leprosy typically involves a small number of surface lesions on the skin. There is generally loss of sensation in these areas, but the other signs and symptoms that occur in multibacillary leprosy are less likely to develop in this form of the disorder.

In any form of leprosy, episodes called reactions can occur, and can lead to further nerve damage. These episodes can include reversal reactions, which involve pain and swelling of the skin lesions and the nerves in the hands and feet. People with the more severe forms of leprosy can develop a type of reaction called erythema nodosum leprosum (ENL). These episodes involve fever and painful skin nodules. In addition, painful, swollen nerves can occur. ENL can also lead to inflammation of the joints, eyes, and the testicles in men.

Leprosy has long been stigmatized because of its infectious nature and the disfigurement it can cause. This stigma can cause social and emotional problems for affected individuals. However, modern treatments can prevent leprosy from getting worse and spreading to other people. While the infection is curable, nerve and tissue damage that occurred before treatment is generally permanent.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Combinations of many variations in genes involved in the immune system affect a person's likelihood of contracting Mycobacterium leprae infection if exposed to the bacteria. Gene variations affecting the immune system also help determine the form of leprosy that individuals develop if the Mycobacterium leprae infection takes hold.

The body's initial, nonspecific response to an invading organism (innate immune response) is its first line of defense against Mycobacterium leprae. If this is followed by an immune system response specific to Mycobacterium leprae infection (adaptive immune response) that restricts the spread of the bacteria, an individual will probably develop the less severe paucibacillary form or not develop leprosy at all. If little or no adaptive immune response occurs, the bacteria can spread widely on the body, traveling through the skin and into the peripheral nerves, and sometimes into deeper tissues, leading to the more severe signs and symptoms of multibacillary leprosy.

Variations in immune system-related genes also affect the likelihood of developing episodes of reaction. Reactions occur when the immune system generates inflammation in response to dead bacteria that are still in the body.

The genes involved in leprosy provide instructions for making proteins that are involved in immune system processes such as recognition of the bacteria, immune system signaling, initiation of inflammation by the innate immune system, and production by the adaptive immune system of immune proteins (antibodies) specific to Mycobacteria leprae. The combined effect of the gene variations, as well as nongenetic factors that are not well understood, determine the effectiveness of these processes and the individual's vulnerability to leprosy.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Leprosy is not inherited, but people can inherit an increased risk of contracting leprosy if they are exposed to the Mycobacterium leprae bacteria. Susceptibility tends to run in families, but the inheritance pattern is unknown.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

About 250,000 new cases of leprosy are diagnosed every year. The condition occurs worldwide, but is most common in India, Brazil, and other areas with warm climates. Between 100 and 250 new cases per year occur in the United States.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Peripheral neuropathy · Very frequent (99-80%)

Peripheral neuropathy is a general term for any disorder of the peripheral nervous system. The main clinical features used to classify peripheral neuropathy are distribution, type (mainly demyelinating versus mainly axonal), duration, and course.

Abnormal autonomic nervous system physiology · Frequent (79-30%)

A functional abnormality of the autonomic nervous system.

Acral ulceration · Frequent (79-30%)

A type of digital ulcer that manifests as an open sore on the surface of the skin at the tip of a finger or toe.

Anti-sphingolipid antibody positivity · Frequent (79-30%)

The presence of autoantibodies (immunoglobulins) in the blood circulation that react against sphingolipids.

Dissociated sensory loss · Frequent (79-30%)

A pattern of sensory loss with selective loss of touch sensation and proprioception without loss of pain and temperature, or vice-versa.

Enlarged peripheral nerve · Frequent (79-30%)

Increase in size of a peripheral nerve. This finding can be appreciated by palpation along the axis of the nerve.

Entrapment neuropathy · Frequent (79-30%)

Malfunction of a peripheral nerve resulting from mechanical compression of the nerve roots from internal or external causes and leading to a conduction block or axonal loss.

Hyperkeratosis · Frequent (79-30%)

Hyperkeratosis is a histopathological term defining a thickened stratum corneum and may be present in many different skin conditions, with many possible overlaps. Hyperkeratosis refers to the increased thickness of the stratum corneum, the outer layer of the skin. Hyperkeratosis is subclassified as orthokeratotic or parakeratotic. Orthokeratotic hyperkeratosis refers to the thickening of the keratin layer with preserved keratinocyte maturation, while parakeratotic hyperkeratosis shows retained nuclei as a sign of delayed maturation of keratinocytes.

Other findings in the same source

From: Orphanet

Additional reported features include Hypohidrosis (Frequent (79-30%)); Hypopigmented macule (Frequent (79-30%)); Impaired temperature sensition (Frequent (79-30%)); Paresthesia (Frequent (79-30%)); Skeletal muscle atrophy (Frequent (79-30%)); Skin nodule (Frequent (79-30%)); Sparse body hair (Frequent (79-30%)); Acute episodes of neuropathic symptoms (Frequent (79-30%)); Abnormality of facial skeleton (Occasional (29-5%)); Abnormality of the seventh cranial nerve (Occasional (29-5%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Leprosy is Infectious Diseases, with a general physician / infectious disease specialist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Which exposure or organism is suspected, and what evidence would confirm it?
• Are precautions, vaccination or advice for close contacts relevant to this infection?
• What should happen if symptoms worsen or do not improve as expected?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.