Intestinal amyloidosis: how it manifests itself

Intestinal amyloidosis develops when fibrillar amyloid protein is deposited in the extracellular space of the intestinal wall, disrupting its structure and function. Manifestations depend on the amount of deposits, their distribution, and the involvement of blood vessels and the neuromuscular system, so the clinical picture can range from virtually asymptomatic to severe, with bleeding or pseudo-obstruction. [1]

If amyloid predominantly infiltrates the mucosa, symptoms of malabsorption often develop: diarrhea, weight loss, steatorrhea, and sometimes signs of bacterial overgrowth in the small intestine. In this situation, the complaints often present as "chronic diarrhea of unknown origin" and can be mistakenly interpreted as a functional disorder or inflammatory bowel disease. [2]

If the blood vessels (including those of the submucosa) are significantly affected, the mucosa becomes fragile and prone to erosions, ulcers, and hemorrhages. Then, latent or overt gastrointestinal bleeding, anemia, sometimes ischemic ulcers, and, less commonly, perforation become more common. [3]

If amyloid is deposited in the nerve plexuses and muscle layer, motility is impaired: pronounced bloating, early satiety, constipation, episodes of stagnation, alternating constipation and diarrhea appear, and in severe cases, chronic intestinal pseudo-obstruction, which often responds poorly to prokinetics and is considered an unfavorable sign. [4]

Table 1. Where do the symptoms of intestinal amyloidosis come from?

Preferential zone of deposits	What is being violated?	How does it feel?
Mucous membrane	absorption, barrier function	diarrhea, steatorrhea, weight loss, deficiencies
Vessels	blood supply, strength of the mucous membrane	occult blood, bleeding, anemia, ulcers
Nerve plexuses	coordination of peristalsis	alternating constipation and diarrhea, pain, pseudo-obstruction
Muscular layer	content promotion	severe constipation, bloating, congestion, obstruction
Local "amyloidomas"	narrowing of the lumen, ulceration above the lesion	symptoms of obstruction, bleeding, pain

[5]

The main clinical syndromes of intestinal amyloidosis

In practice, symptomatic intestinal amyloidosis most often consists of several recurring syndromes. These include gastrointestinal bleeding, malabsorption, protein-losing enteropathy, and chronic dysmotility, including pseudo-obstruction. This approach is convenient because it immediately suggests which symptoms to expect and which complications are most likely. [6]

Bleeding syndrome may manifest as occult blood loss (weakness, decreased hemoglobin) or overt episodes of blood in the stool, melena, and, less commonly, massive bleeding. The mechanism is usually associated with erosions, ulcers, submucosal hemorrhages, and vascular fragility, and massive occult bleeding has also been described in certain variants of amyloidosis. [7]

Malabsorption syndrome most often presents with chronic diarrhea, weight loss, loss of appetite, steatorrhea, bloating, and gas. Causes include mucosal infiltration, motility disorders with bacterial overgrowth, and possible pancreatic involvement, so symptoms may be "mixed" and fluctuate. [8]

Protein-losing enteropathy presents with a combination of gastrointestinal symptoms and signs of protein loss: peripheral edema, sometimes ascites, and weakness. The key clinical implication is that edema in this condition occurs not because of the heart, liver, or kidneys, but because protein is lost through the gastrointestinal mucosa. [9]

Table 2. 4 leading syndromes and typical manifestations

Syndrome	Leading complaints	Frequent "hints"
Bleeding	blood in the stool, melena, weakness	anemia, fragile mucous membranes, ulcers
Malabsorption	diarrhea, steatorrhea, weight loss	deficiencies, bloating, bacterial overgrowth
Protein-losing enteropathy	diarrhea plus swelling	low albumin, ascites
Dysmotility and stagnation	constipation, bloating, nausea, pain	pseudo-obstruction, poor response to prokinetics

[10]

What exactly do "intestinal" symptoms look like: stool, pain, bloating, blood

The most common complaint with intestinal damage is a change in bowel habits. Diarrhea, constipation, or alternating diarrhea and constipation are possible, with the same patient potentially switching from "accelerated transit" to severe stagnation as neuromuscular damage progresses. [11]

Diarrhea associated with intestinal amyloidosis can be watery or oily (steatorrhea). For the patient, this manifests as frequent bowel movements that are difficult to manage with dietary restrictions, often accompanied by weight loss and weakness, and sometimes combined with episodes of incontinence. [12]

Constipation and severe bloating are most often associated with dysmotility, when the intestines become "sluggish" and poorly move their contents. In severe cases, pseudo-obstruction develops: severe distension, pain, nausea and vomiting, lack of stool and gas, and no visible mechanical obstruction. [13]

Blood in the stool and occult blood loss are possible with damage to the blood vessels and mucous membranes. Clinically, this manifests as blood, dark stool, weakness, dizziness, and progressive anemia. Sometimes, bleeding is the first symptom that leads to examination. [14]

Table 3. Symptom and most likely mechanism

Symptom	What is most often the basis?	What usually accompanies
Watery diarrhea	mucositis, dysmotility, rapid transit	weight loss, weakness
Steatorrhea	fat malabsorption, bacterial overgrowth	bloating, deficiencies
Persistent constipation	neuromuscular lesion	bloating, early satiety
Attacks of pseudo-obstruction	severe intestinal neuropathy and myopathy	pain, vomiting, no gas
Blood in the stool, anemia	vascular fragility, erosions and ulcers	weakness, dizziness

[15]

Manifestations by intestinal sections and “masks” of other diseases

The small intestine is affected more often than other parts of the body, so it is here that malabsorption, accompanied by diarrhea, steatorrhea, and weight loss, often develops. The small intestine can also cause bleeding and signs of congestion, so the clinical picture can appear paradoxical: for example, alternating diarrhea and constipation with severe bloating. [16]

Colonic amyloidosis can present with persistent constipation, bloating, and pain, as well as bleeding from the distal sections. An important clinical feature: colonic lesions can mimic inflammatory bowel disease, ischemic colitis, or tumor, as the mucosa is fragile, with erosions and ulcers, and the presentation can be segmental. [17]

Amyloidosis can manifest as a localized "mass" in the intestinal wall, narrowing the lumen and leading to obstructive symptoms or bleeding from the ulcerated mucosa overlying the lesion. Externally, it often appears as a tumor until pathological confirmation is obtained. [18]

Clinically, it's important to remember that intestinal symptoms often coexist with general manifestations of systemic amyloidosis: weakness, weight loss, low blood pressure, neurological symptoms, and signs of kidney or heart damage. This combination increases the likelihood that "ordinary diarrhea" or "ordinary constipation" has a systemic cause. [19]

Table 4. Where deposits appear most often and what they look like

Department	What occurs more often?	What "masks" are possible?
Small intestine	diarrhea, steatorrhea, weight loss, deficiencies	celiac disease, chronic infection, bacterial overgrowth
Colon	constipation, bloating, pain, blood	inflammatory bowel disease, ischemic colitis, tumor
Distal sections	bleeding, tenesmus	hemorrhoidal disease, proctitis of other origin
Neuromuscular apparatus	pseudo-obstruction	mechanical obstruction, adhesive disease
Local "amyloidoma"	obstruction, bleeding	tumor

[20]

Severe manifestations and signs requiring urgent evaluation

Pseudo-obstruction is considered one of the most severe manifestations of intestinal amyloidosis. It is dangerous due to rapid dehydration, electrolyte imbalances, the risk of aspiration during vomiting, and severe intoxication. However, visualization reveals no "plug" because the problem is functional: the intestinal neuromuscular system ceases to function in a coordinated manner. [21]

Gastrointestinal bleeding in amyloidosis is dangerous because it can be hidden and prolonged, leading to severe anemia, or sudden and massive. If weakness, dizziness, black stool, or blood in the stool occurs, it should be assessed as a potentially significant bleed rather than simply left to "go away on its own." [22]

Ulceration and ischemia of the intestinal wall due to vascular damage sometimes lead to perforation, although this is a rare but extremely dangerous complication. Clinically, sudden, stabbing pain, abdominal muscle tension, fever, and signs of peritonitis are alarming. [23]

Protein-losing enteropathy is dangerous because it creates a picture of generalized edema and ascites and can increase weakness, reduce treatment tolerance, and increase the risk of infectious complications. If edema is combined with diarrhea and decreased albumin, intestinal protein loss should be considered as a possible cause. [24]

Table 5. Red flags for suspected intestinal amyloidosis

Sign	Why is it dangerous?	What is often behind this?
Vomiting plus lack of stool and gas, severe bloating	risk of pseudo-obstruction and severe electrolyte disturbances	neuromuscular lesion
Blood in stool or black stool	risk of significant bleeding	vascular fragility, ulcers
Rapid increase in weakness and anemia	hidden prolonged bleeding is possible	chronic blood loss
Sudden sharp pain and signs of peritonitis	risk of perforation	ischemic ulcers and necrosis
Edema and ascites associated with diarrhea	risk of protein-losing enteropathy	protein loss through the mucous membrane

[25]

How are manifestations related to the type of amyloidosis?

Symptoms of intestinal amyloidosis often correlate with the type of amyloid and the structures primarily affected. Clinical reviews note that amyloidosis of the serum amyloid A (AA) protein most often causes diarrhea and malabsorption, while amyloidosis of the immunoglobulin light chain (AL) often presents with constipation, mechanical obstruction, or chronic pseudo-obstruction. [26]

Transthyretin amyloidosis (ATTR) and beta-2 microglobulin amyloidosis (Aβ2M, dialysis-associated) can also involve the gastrointestinal tract, but the clinical features differ. In particular, significant gastrointestinal bleeding has been described in the dialysis-associated variant, while in ATTR, intestinal manifestations can be combined with systemic signs of nervous system and cardiac damage. [27]

Localized intestinal amyloidosis exists separately, which can manifest as a solitary tumor-like formation or a limited area of lesion. Clinically, it most often presents as localized pain, bleeding, or signs of partial obstruction, while there may be no signs of systemic involvement. [28]

The practical significance of this "typical" logic of manifestations is that it helps explain paradoxes. For example, one patient may experience diarrhea and weight loss, while another with the same diagnosis may experience persistent constipation and pseudo-obstruction. This may reflect different types of amyloid and different targets in the intestinal wall. [29]

Table 6. Type of amyloidosis and the most typical intestinal “phenotype”

Amyloid type	Full name	What is more often clinically dominant?
AL	immunoglobulin light chain amyloidosis	constipation, congestion, obstruction, pseudo-obstruction
AA	serum amyloid A protein amyloidosis	diarrhea, malabsorption, weight loss
ATTR	transthyretin amyloidosis	variable, often against the background of systemic damage
Aβ2M	beta-2 microglobulin amyloidosis, dialysis-associated	bleeding and other gastrointestinal manifestations according to reviews
Localized	limited deposits in the intestinal wall	tumor-like "mass", local pain, bleeding

[30]