Primary localized cutaneous amyloidosis

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Primary localized cutaneous amyloidosis (PLCA) is a condition in which clumps of abnormal proteins called amyloids build up in the skin, specifically in the wave-like projections (dermal papillae) between the top two layers of skin (the dermis and the epidermis). The primary feature of PLCA is patches of skin with abnormal texture or color. The appearance of these patches defines three forms of the condition: lichen amyloidosis, macular amyloidosis, and nodular amyloidosis.

Lichen amyloidosis is characterized by severely itchy patches of thickened skin with multiple small bumps. The patches are scaly and reddish brown in color. These patches usually occur on the shins but can also occur on the forearms, other parts of the legs, and elsewhere on the body.

In macular amyloidosis, the patches are flat and dark brown. The coloring can have a lacy (reticulated) or rippled appearance, although it is often uniform. Macular amyloidosis patches are most commonly found on the upper back, but they can also occur on other parts of the torso or on the limbs. These patches are mildly itchy.

Nodular amyloidosis is characterized by firm, raised bumps (nodules) that are pink, red, or brown. These nodules often occur on the face, torso, limbs, or genitals and are typically not itchy.

In some affected individuals, the patches have characteristics of both lichen and macular amyloidosis. These cases are called biphasic amyloidosis.

In all forms of PLCA, the abnormal patches of skin usually arise in mid-adulthood. They can remain for months to years and may recur after disappearing, either at the same location or elsewhere. Very rarely, nodular amyloidosis progresses to a life-threatening condition called systemic amyloidosis, in which amyloid deposits accumulate in tissues and organs throughout the body.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

PLCA can be caused by mutations in the OSMR or IL31RA gene. When caused by an OSMR gene mutation, the condition is classified as type 1, while an IL31RA gene mutation causes type 2. Mutations in either gene are likely involved in lichen and macular amyloidosis, which are thought to be related conditions that arise through similar disease mechanisms. The genetic basis of nodular amyloidosis is unknown.

The OSMR and IL31RA genes provide instructions for making parts (subunits) of the interleukin-31 (IL-31) receptor. The subunit produced from OSMR can also pair with a different protein to form the OSM receptor type II. Both receptors are embedded in the membrane of cells throughout the body. Each attaches to a particular protein, fitting together like a lock and its key. This attachment triggers a series of chemical signals inside the cell that directs certain cell functions.

OSM receptor type II interacts with a protein called oncostatin M (OSM). Signaling triggered by OSM appears to play a role in many body processes, including the development of blood cells, the maturation of cells to become certain cell types, an immune system response called inflammation, and the self-destruction (apoptosis) of cells. The IL-31 receptor interacts with IL-31, triggering signaling that promotes inflammation and itch (pruritus). OSMR gene mutations reduce signaling stimulated by OSM and IL-31, while IL31RA gene mutations impair only IL-31 signaling.

How PLCA develops is not completely understood. In lichen and macular amyloidosis, it is thought that scratching the itchy skin causes skin cells to undergo apoptosis, releasing proteins that abnormally clump together and form amyloids. The proteins that make up the amyloids are abnormal versions of proteins called keratins. The role of gene mutations in this process is still being determined. Because signaling triggered by IL-31 normally stimulates itching, it is unclear how a reduction of this signaling is involved in itchy skin. Also unclear is how reduced IL-31 signaling is related to apoptosis or amyloid formation. Researchers speculate that a reduction of signaling triggered by OSM may make cells more likely to undergo apoptosis, which may promote amyloid buildup.

In nodular amyloidosis, the amyloids are composed of abnormal versions of proteins called immunoglobulin light chains released from certain blood cells called plasma cells. However, it is unknown how this form of PLCA develops.

Many people with PLCA do not have a mutation in the OSMR or IL31RA gene. The cause of the condition in these cases is unknown.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

In most cases, PLCA is not inherited and occurs in people with no history of the condition in their family.

When the condition runs in families, it is usually inherited in an autosomal dominant pattern, which means one copy of the altered OSMR or IL31RA gene in each cell is sufficient to cause the disorder. In these cases, the affected person has one parent with the condition.

Rarely, when caused by a mutation in the OSMR gene, PLCA is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

PLCA occurs worldwide, most commonly in Southeast Asia and South America. The prevalence of the condition is unknown.

Which doctor should you see?

The suggested department for discussing Primary localized cutaneous amyloidosis is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

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.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Primary localized cutaneous amyloidosis. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

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.