AL amyloidosis
(Immunoglobulin Light-Chain Amyloidosis)

Article written and reviewed by Dr Luca Moretti

AL amyloidosis, also known as primary systemic immunoglobulin light-chain amyloidosis, is a rare systemic disease belonging to the amyloidoses and characterized by extracellular deposition of amyloid fibrils composed of monoclonal immunoglobulin light-chain fragments produced in excess by an abnormal plasma cell clone.

AL amyloidosis is a plasma cell or, more rarely, lymphoplasmacytic dyscrasia defined by organ damage caused by amyloidogenic light chains. It may coexist with multiple myeloma, but it cannot properly be classified as MGUS when the clone causes amyloid deposition and organ dysfunction. It may involve many organs, particularly the heart, kidneys, liver, peripheral nervous system and gastrointestinal tract.

Structurally, the disease is defined by insoluble amyloid deposits, a fibrillar protein substance with a characteristic affinity for Congo red on light microscopy and typical apple-green birefringence under polarized light. Formation of these fibrils results from conformational instability and the propensity to aggregate of specific light chains, predominantly lambda but also kappa, produced by expanded pathologic plasma cell clones.

The epidemiology of AL amyloidosis parallels the distribution of monoclonal gammopathies, with an estimated incidence of approximately 9 to 14 cases per million people per year in Western countries and prevalence estimates varying by population and period, broadly around 40 to 70 cases per million in recent Western datasets.
The mean age at diagnosis is generally 60 to 70 years, with a slight male predominance. Cases are also described at younger ages, particularly in association with multiple myeloma. Historically, AL amyloidosis was the most frequently diagnosed systemic form, but its relative proportion varies among series and has decreased with increasing recognition of ATTR amyloidosis; prognosis remains particularly poor in the presence of cardiac involvement.

Diagnostic delay is common, averaging more than one year from symptom onset because of the heterogeneous and often subtle clinical presentation. The true incidence is probably underestimated because of both diagnostic difficulty and failure to recognize paucisymptomatic or oligosymptomatic forms.

Etiology, pathogenesis and pathophysiology

The etiology of AL amyloidosis is pathologic production of monoclonal light chains, lambda or less commonly kappa, by an expanded clone of neoplastic plasma cells within the bone marrow.
The clone is often small and may not meet the tumor-burden criteria for multiple myeloma; nevertheless, AL amyloidosis attributable to the clone defines clinically significant disease rather than MGUS.
Production of an amyloidogenic monoclonal light chain is necessary but is not sufficient by itself: fibril formation and organ damage depend on protein properties, concentration, tissue susceptibility and other biologic factors.

No specific environmental or familial factors have been defined that allow AL amyloidosis to be predicted. Risk increases with age and the presence of a monoclonal gammopathy, but only a small proportion of clones produce light chains with amyloidogenic properties.
Not all patients with monoclonal gammopathy therefore develop AL amyloidosis: specific sequence and conformational properties of light chains contribute to their propensity to aggregate, but no universal set of required mutations has been defined.

From a pathogenetic standpoint, the fundamental mechanism is production and release into the circulation of free light chains by the pathologic plasma cell clone.
Some of these chains, because of particular amino-acid sequence characteristics and three-dimensional conformation, are unstable and tend to adopt an abnormal beta-sheet-rich structure. This conformation facilitates self-aggregation of light chains into protofibrils and then mature amyloid fibrils, which are insoluble and resistant to physiologic proteolytic degradation.
Fibrillogenesis initially occurs in the extracellular space, near blood vessels, and may continue locally with further enlargement of deposits. Molecular biology studies have identified certain hypervariable regions of lambda light chains, particularly VL segments, as important determinants of amyloidogenic propensity.

In parallel with aggregation, amyloid fibrils recruit supporting proteins, including serum amyloid P component, apolipoproteins E and A-IV, laminin, fibronectin and glycosaminoglycans, contributing to the stability and persistence of deposits in tissues. The result is progressive interstitial infiltration of involved organs, with disruption and alteration of normal tissue architecture.

From a pathophysiologic standpoint, the consequences are directly related to the extent, site and rate of amyloid accumulation.
In the heart, interstitial fibril deposition causes ventricular wall thickening and stiffness, impaired diastolic compliance and progressive development of restrictive cardiomyopathy with early diastolic dysfunction that evolves to refractory heart failure.
In the kidney, amyloid accumulates mainly in the glomeruli, causing nephrotic-range proteinuria, progressive deterioration of renal function and, in advanced cases, end-stage renal disease.
The liver may be involved through infiltration of sinusoids and parenchyma, causing hepatomegaly and hepatic dysfunction; the peripheral nervous system is frequently affected with sensorimotor polyneuropathy and autonomic neuropathy. In the gastrointestinal tract, deposition may cause malabsorption, motility abnormalities, bleeding and variable symptoms.

The final effect is structural and functional damage to involved organs, related both to the physical burden of fibrillar deposits and to direct toxicity exerted by soluble light chains and their protofibrillar precursors. It is now recognized that, particularly in the heart, free light chains can induce cellular dysfunction and apoptosis through oxidative stress, mitochondrial metabolic disturbance, dysregulation of intracellular calcium and activation of inflammatory pathways.

The clinical heterogeneity of AL amyloidosis therefore depends on an interplay among the biochemical characteristics of the light chains produced, their quantity, individual organ susceptibility to amyloid infiltration and the biologic response to deposits. This accounts for the variability of clinical presentation, discussed in the next section.

Clinical manifestations

AL amyloidosis is characterized by an extremely heterogeneous clinical presentation, reflecting the ability of amyloid to infiltrate and impair the function of numerous organs and tissues. Initial symptoms are often subtle and nonspecific, including fatigue, unintentional weight loss, weakness and vague complaints that may precede recognition of the disease by months or years. Multiorgan involvement is common, although disease may occasionally present with a single dominant symptom depending on the predominant site of deposition.

The heart is one of the organs most frequently involved, and cardiac involvement is the major prognostic determinant. Myocardial amyloid deposition typically leads to restrictive cardiomyopathy, with progressive exertional dyspnea, orthopnea, dependent edema and easy fatigability. Physical examination may reveal jugular venous distention, basal pulmonary crackles, ascites and, in advanced cases, refractory congestive heart failure. Advanced disease may also cause arterial hypotension and, when autonomic neuropathy is present, orthostatic hypotension. Involvement of the conduction system may cause arrhythmias, atrioventricular block and syncope.

The kidney is another major target: glomerular amyloid deposition manifests as nephrotic-range proteinuria, often above 3.5 g/day, peripheral edema, hypoproteinemia and hyperlipidemia, followed by progressive decline in renal function to end-stage renal disease. Dependent edema, ascites and, in advanced cases, signs of uremia are common on physical examination.

The liver may show amyloid infiltration with hepatomegaly, often firm and painless, laboratory abnormalities including increased alkaline phosphatase and, more rarely, transaminases, and in rare cases hepatic failure. Palpation may reveal a rounded liver edge extending below the costal margin.

Involvement of the peripheral nervous system manifests as a symmetric sensorimotor polyneuropathy characterized by distal paresthesias, hypoesthesia, motor deficits and, in advanced cases, muscle atrophy. Autonomic neuropathy may be present and is clinically important; it can cause orthostatic hypotension, sphincter dysfunction, sweating abnormalities, erectile dysfunction and gastroparesis. The Achilles reflex may be lost early, while vibratory and pain sensation are markedly reduced.

The gastrointestinal tract may produce subtle and variable symptoms: weight loss, diarrhea, malabsorption, constipation, early satiety, gastrointestinal bleeding due to vascular fragility and, with marked involvement, malabsorption syndrome with nutritional deficiencies and cachexia. Macroglossia is a suggestive but not pathognomonic finding in AL amyloidosis.

Cutaneous manifestations include petechiae, periorbital purpura, or “raccoon eyes”, ecchymoses and, in advanced cases, soft-tissue infiltration with nodules, skin thickening and a waxy appearance. Articular manifestations may include joint pain, stiffness, swelling and carpal tunnel syndrome, often bilateral, caused by amyloid deposition in perineural tissues.

Additional manifestations include pulmonary involvement with dyspnea and pleural effusions, mucosal hemorrhage, spontaneous bleeding, malabsorption, coagulation abnormalities such as factor X deficiency due to amyloid sequestration, and severe hypotension. Clinical presentation is often dominated by nonspecific symptoms that delay recognition, such as worsening fatigue, weight loss, diffuse edema and signs of multiorgan failure.

Taken together, the clinical manifestations of AL amyloidosis result directly and indirectly from progressive amyloid infiltration of tissues, impairment of organ function and the toxic effects of free light chains, with substantial interindividual variability in severity and rate of progression. Early recognition of typical signs and symptoms is a crucial clinical challenge and is essential to improving the prognosis of a disease that, when not recognized and treated promptly, may rapidly progress to multiorgan failure and death.

Investigations and diagnosis

Diagnosis of AL amyloidosis is a major clinical challenge because of the wide range of possible presentations and the absence of pathognomonic symptoms in early stages. Clinical suspicion should arise in the presence of multiorgan syndromes characterized by rapidly progressive restrictive heart failure, unexplained nephrotic syndrome, sensorimotor polyneuropathy associated with autonomic dysfunction, macroglossia, bilateral carpal tunnel syndrome, hepatomegaly and, more generally, any constellation of systemic symptoms in a patient with known or suspected monoclonal gammopathy.

Initially, laboratory testing plays a central role: indirect signs of organ damage are sought, including proteinuria, renal failure, elevated transaminases or alkaline phosphatase, increased NT-proBNP and troponin and coagulation abnormalities, together with markers of monoclonality such as serum and urine electrophoresis with immunofixation, which are essential for detecting a monoclonal light-chain component, kappa or lambda.

Serum free light-chain quantification assesses both the presence of clonality and the magnitude of abnormal production. Identification of a monoclonal component is not, however, sufficient to diagnose amyloidosis, and must be integrated with imaging and, above all, histologic demonstration of deposits.

Echocardiography is central to assessing cardiac involvement: it may reveal symmetric ventricular wall thickening, a granular appearance, atrial dilation, diastolic dysfunction and reduced global longitudinal strain with relative apical sparing, a characteristic pattern of amyloid cardiomyopathy.

Electrocardiography frequently shows low QRS voltages, a pseudoinfarction pattern and conduction abnormalities.

Other useful tools include cardiac magnetic resonance imaging, with diffuse late gadolinium enhancement, and bone scintigraphy using diphosphonate tracers, useful in the differential diagnosis with transthyretin amyloidosis.

Renal or hepatic biopsy may be required in selected cases, especially when biopsies from surrogate sites are nondiagnostic or direct documentation and typing of organ involvement is needed.

Definitive diagnosis of AL amyloidosis is based on histologic demonstration of amyloid deposits in affected tissues or accessible sites such as periumbilical fat, by subcutaneous fat biopsy, rectal mucosa or bone marrow.
Tissues are stained with Congo red and examined by light microscopy, where amyloid deposits appear as amorphous extracellular material with characteristic apple-green birefringence under polarized light.
Once amyloid is confirmed, immunohistochemical typing or mass spectrometry is essential to identify the AL nature of the fibrils. The mere presence of amyloid deposits without identification of the type is not sufficient for diagnosis and targeted treatment.

At the same time, the clone must be evaluated by bone marrow aspiration and biopsy. A plasma cell proportion of 10% or more does not by itself define active multiple myeloma: IMWG criteria, including myeloma-defining events or attributable CRAB damage, must be applied. In AL amyloidosis, the clone may involve less than 10% of marrow cells but remains clinically significant.

The diagnosis of AL amyloidosis requires integration of the following elements:

• histologic documentation of amyloid deposits,
• confirmation of the AL nature of deposits by immunohistochemistry or mass spectrometry,
• identification of a monoclonal light-chain component in serum, urine or bone marrow,
• exclusion of other forms of systemic amyloidosis, particularly transthyretin amyloidosis (ATTR).

Supportive findings include macroglossia, bilateral carpal tunnel syndrome, a suggestive clinical picture, characteristic echocardiographic and magnetic resonance abnormalities, and compatible patterns of proteinuria and neuropathy, but without histologic confirmation and AL typing the diagnosis remains probable rather than definitive.

Timely and accurate diagnosis is essential to start treatment early and improve prognosis, given the high risk of multiorgan failure and rapid progression, especially in forms with cardiac involvement.

Treatment and prognosis

Treatment of AL amyloidosis is one of the most complex challenges in modern medicine because it must combine control of the plasma cell clone responsible for amyloidogenic light-chain production, management of organ manifestations and support of compromised vital functions. The primary therapeutic objective is rapid, deep and durable suppression of monoclonal light-chain production, thereby stopping formation and deposition of new amyloid fibrils, preventing worsening organ dysfunction and, when possible, allowing regression of existing deposits.

First-line treatment must be adapted to cardiac stage, organ function and patient eligibility. For many newly diagnosed patients, the standard includes daratumumab combined with bortezomib, cyclophosphamide and dexamethasone; alternative regimens are selected when this combination is contraindicated or not tolerated.

High-dose chemotherapy followed by autologous hematopoietic stem cell transplantation is a first-line or consolidation option for a carefully selected minority of patients with adequate organ reserve; it is not a universal standard. Rigorous selection is essential to limit treatment-related mortality.

Supportive therapies are fundamental. In cardiac involvement, the cornerstone consists of diuretics and individualized sodium restriction; beta blockers, ACE inhibitors, angiotensin receptor blockers and other vasodilators are often poorly tolerated because of hypotension and low cardiac output and should be used only for selected indications. Nephropathy, autonomic neuropathy and other manifestations require specific organ support.

Antibodies directed against deposits remain investigational: NEOD001 did not demonstrate benefit in registrational trials; moreover, phase III CARES studies of CAEL-101 did not meet the primary endpoint in the overall population. CAEL-101 is not approved for routine clinical use. Agents that stabilize light-chain structure or inhibit amyloid aggregation remain an important research frontier but are not yet approved for routine clinical use.

Follow-up requires monitoring of hematologic response using free light chains and immunofixation and of organ response using cardiac biomarkers, renal function, proteinuria and targeted assessments. Standard hematologic categories include complete response, very good partial response, partial response and no response; repeat bone marrow assessment is reserved for clinical indications.

The prognosis of AL amyloidosis remains serious, with median survival in untreated patients with advanced cardiac involvement not exceeding approximately 6 to 12 months. Modern therapeutic strategies have nevertheless substantially improved survival, with complete or very good responses in more than 50 to 60% of successfully treated patients. Prognosis depends closely on the extent and severity of organ involvement, especially cardiac involvement, age, speed of treatment initiation and early hematologic response. Biomarkers such as NT-proBNP and troponin are now used to stratify risk and guide therapeutic choice.

Despite therapeutic advances, relapse is common and requires salvage, or second-line, strategies that may include reuse of bortezomib-based regimens, immunomodulatory agents such as lenalidomide and pomalidomide, or investigational agents, always according to patient tolerance and residual organ function.

Multidisciplinary integration involving hematologists, cardiologists, nephrologists, neurologists and hepatologists is fundamental to provide an individualized approach, maximize the probability of remission and improve quality of life in patients with this complex systemic disease.

Complications

The complications of AL amyloidosis are numerous and are key determinants of prognosis and quality of life. They arise from structural and functional damage caused by amyloid deposits in different organs, from the toxic effects of free light chains and from direct and indirect consequences of treatment. Complications may occur at any stage of disease, from diagnosis to relapse, and can involve all major organs and systems.

The most feared and frequent complication is cardiac involvement, which causes progressive restrictive heart failure, often rapidly worsening and refractory to conventional treatment. Arrhythmias, especially atrial fibrillation, ventricular tachyarrhythmias and atrioventricular blocks, conduction disturbances and syncope occur because of infiltration of the conduction system and direct light-chain injury, increasing the risk of sudden death. In some cases, acute deterioration of ventricular function develops with acute pulmonary edema and cardiogenic shock.

The kidney may progress rapidly to end-stage chronic kidney disease as a consequence of massive proteinuria and amyloid glomerulosclerosis. Secondary complications include nephrotic syndrome with hypoproteinemia and hypercoagulability, susceptibility to urinary infections and the need for renal replacement therapy with dialysis and its associated problems. Volume depletion secondary to protein loss and diuretics may further worsen hypotension.

When involved, the liver may develop hepatic failure, portal hypertension, coagulopathy due to impaired synthesis of coagulation factors and sequestration of factor X by amyloid deposits, ascites and a risk of gastrointestinal bleeding.

Neurologic complications include worsening sensorimotor polyneuropathy, with progressive loss of independent mobility, traumatic falls, autonomic neuropathy with severe orthostatic hypotension, syncope, sphincter dysfunction and gastrointestinal motility disorders such as gastroparesis and paralytic ileus. Autonomic neuropathy, which is often underestimated, can contribute substantially to morbidity and the risk of sudden death.

At the hematologic and systemic level, protein loss and vascular amyloid deposition may cause coagulation abnormalities with an increased risk of spontaneous bleeding, including petechiae, ecchymoses, periorbital purpura, mucosal bleeding and gastrointestinal hemorrhage, particularly in acquired factor X deficiency. At the same time, nephrotic syndrome and chronic inflammation may cause hypercoagulability, predisposing to deep-vein thrombosis, pulmonary embolism and microvascular thrombosis.

Infectious complications are frequent and serious, promoted by immunosuppression due to the disease and cytotoxic treatments: pneumonia, sepsis, urinary and respiratory tract infections and opportunistic infections, particularly in patients undergoing autologous stem cell transplantation. Chemotherapy-induced neutropenia further increases infectious risk and requires careful monitoring and prompt treatment.

Other neurologic and musculoskeletal complications include carpal tunnel syndrome, which is frequently bilateral and recurrent, macroglossia with risk of airway obstruction and feeding difficulty, and progressive muscle weakness with atrophy in advanced neuropathy.

Disease relapse and treatment resistance are serious complications: progression of the plasma cell clone, acquisition of resistant mutations and loss of treatment efficacy can cause therapeutic failure and worsening prognosis. Management of relapse requires salvage strategies, often less effective and more toxic than previous lines.

Iatrogenic complications from treatment, including chemotherapy, stem cell transplantation and immunosuppression, include myelosuppression, cytopenias, organ toxicity, allergic drug reactions, neurologic toxicity and a risk of secondary neoplasms. The frailty of patients with AL amyloidosis requires careful balancing of therapeutic efficacy and tolerability.

Finally, psychological and social complications, including anxiety, depression, loss of independence and social isolation, are often neglected but highly relevant to quality of life and adherence to treatment and require integrated multidisciplinary support.

Management of complications, together with etiologic treatment of the disease, is a cornerstone of comprehensive care for patients with AL amyloidosis, with the aim of improving survival, organ function and quality of life.

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