Lymphman - Symbol of Adult-Onset PIL Awareness

Primary Intestinal Lymphangiectasia: Beyond the Textbooks

Welcome to this platform dedicated to unraveling the complexities of a particular form of a rare medical condition known as adult-onset Primary Intestinal Lymphangiectasia (PIL). A condition so rare that there have been only approximately 50 reported cases of adult-onset PIL since 1961. I’m a man in my early 50s who was diagnosed with this very condition and, as far as I know, the first person in the world to successfully use a drug called Trametinib to reverse lymphangiectasia in the adult-onset form of the disease.

The unexpected arrival of unfamiliar symptoms marked the beginning of my journey with PIL. It was a diagnosis that introduced me to a disease I had never heard of before. The confusion and concern this sparked were significant but served as a catalyst for my determination to understand and manage this condition. As I ventured deeper into the realm of PIL, particularly its adult-onset form, I realized the rarity and lack of comprehensive understanding surrounding it.

This journey and the inability of doctors to effectively manage my symptoms led me to discover and self-administer a novel treatment that has been remarkably successful in managing my adult-onset PIL. However, I recognize that PIL can have multiple causes and I address only one potential cause. This website is a place where I share the hypothesis I've developed about what caused my disease and how my treatment works.

In the following sections, we will explore the world of adult-onset PIL, its symptoms, and the current treatments available. We will also discuss the limitations of these treatments and delve into my hypothesis about the etiology of adult onset PIL. We'll touch upon intriguing topics like RASopathy, Mitogen-Activated Protein Kinase (MAPK) signaling dysregulation, the lymphatic endothelial cell (LEC) differentiation program, and the potential role of MEK inhibitors in reversing PIL.

Primary Intestinal Lymphangiectasia

Primary Intestinal Lymphangiectasia, also recognized as Waldmann's disease, is an uncommon disorder characterized by the dilation of lymphatic vessels within the small intestine. The primary defect in PIL is the inability of the lymphatic system to adequately drain lymph, resulting in an accumulation and leakage of lymph into the intestinal lumen.

History of PIL

The condition was first described by Waldmann in 1961. Since then, it has been primarily diagnosed in infancy or early childhood. However, it's important to note that the disease can also manifest in adults.

Adult-onset PIL vs. Childhood-onset PIL

While the disease is typically diagnosed in infancy or early childhood, adult-onset PIL also occurs and presents a range of symptoms influenced significantly by the extent of protein loss. In children, growth retardation is a common symptom due to nutritional deficiencies developed from malabsorption. In adults, weight loss is more common, along with other symptoms such as chronic diarrhea and malabsorption.

Asymptomatic or Mild Presentations

Interestingly, adult-onset PIL can range from being asymptomatic to severe, implying a broad clinical spectrum. This variability in symptom severity is quite different from the "textbook" presentations often associated with severe cases in adults. Some patients may exhibit minimal or subtle clinical features, diverging from what is typically expected in PIL cases.

Current Treatments for PIL

The mainstay of treatment for PIL is dietary management. This typically involves a high-protein, low-fat diet supplemented with medium-chain triglycerides (MCTs). MCTs are directly absorbed into the portal circulation, bypassing the lymphatic system, thus reducing lymphatic flow and protein loss. However, dietary management is often ineffective in cases of adult-onset PIL.

In cases where dietary management is insufficient, other therapeutic options may be considered. These include Octreotide, Sirolimus, or Anti-plasmin. The administration of Octreotide, Sirolimus, or Anti-plasmin has been shown to provide relief in some cases, but these are not universally effective.

Octreotide: Octreotide is a somatostatin analogue, a hormone that inhibits the release of several other hormones in the body. In the context of PIL, Octreotide can help reduce the flow of lymph and thus decrease the leakage of lymph into the intestine.

Sirolimus: Sirolimus (also called Rapamycin) is an immunosuppressant drug that is often used to prevent organ rejection in transplant patients. It works by inhibiting the mammalian target of rapamycin (mTOR), a protein that regulates cell growth and proliferation. In PIL, Sirolimus might help by reducing the dilation of the lymphatic vessels, thereby improving lymphatic flow.

Anti-plasmin: Anti-plasmin is a drug that inhibits plasmin, an enzyme that breaks down blood clots, which may help reduce the leakage of lymph into the intestinal lumen.

Despite these treatment strategies, PIL is often a chronic disease, and long-term management is required to control symptoms and maintain nutritional status. The mixed effectiveness of these treatments in adults, along with the chronic nature of PIL, underscores the need for a deeper understanding of the disease mechanisms and the development of more effective therapeutic strategies.

My Theory: MAPK Signal Dysregulation and Adult-Onset PIL

I hypothesize that dysregulation of the MAPK signaling pathway may be responsible for some cases of adult-onset PIL. This theory is founded on the understanding that the MAPK pathway is crucial for a variety of cellular processes, including cell growth, proliferation, differentiation, and survival.

The MAPK pathway is particularly important for the differentiation of LECs, a process crucial to maintaining the structure and function of the lymphatic system. Any disruption or dysregulation in this pathway could potentially hinder the proper differentiation of these cells, leading to structural abnormalities in the lymphatic vessels. This, in turn, could result in lymphangiectasia, a characteristic feature of PIL.

One potential source of MAPK pathway dysregulation is the presence of mosaic (only in certain cells) activating (“turns on a switch”) RAS mutations. RAS proteins are a family of related proteins which are vital to transmitting signals within cells (cellular signal transduction). These proteins are often found on the inner surface of the cell's membrane and act as an on/off switch for these signals.

In the context of the MAPK pathway, RAS proteins, when activated by binding with a molecule called guanosine triphosphate (GTP), can trigger a cascade of signals leading to cell proliferation. However, a mosaic activating RAS mutation can cause the RAS protein to become constitutively activated, meaning the GTP remains "on" and the RAS protein is stuck in its active state.

This permanent activation of the RAS protein disrupts the normal signaling process in the MAPK pathway, hindering the proper differentiation of LECs, which requires suppression of ERK (extracellular signal-regulated kinase) signaling to occur, and leading to the dilation of lymphatic vessels seen in PIL.

Understanding the MAPK Pathway

The MAPK pathway is a key signal transduction pathway that transmits signals from the cell surface to the nucleus, leading to a variety of cellular responses, including proliferation, differentiation, survival, and apoptosis.

The MAPK pathway consists of a series of sequentially activated proteins, including RAS, MEK (MAPK/ERK kinase), and ERK. Each of these proteins plays a critical role in transmitting and amplifying the signal through the pathway.

RAS: RAS is a family of related proteins involved in transmitting signals within cells. It acts as a molecular switch, becoming activated when it binds to GTP. When activated, RAS can trigger a cascade of signals leading to, among other things, cell proliferation.

MEK: When RAS is activated, it triggers the activation of a series of proteins, including MEK. MEK is a type of protein kinase, an enzyme that modifies other proteins by chemically adding phosphate groups to them. In the MAPK pathway, MEK specifically phosphorylates and activates ERK.

ERK: ERK is the final protein in the MAPK cascade. Once activated by MEK, ERK can enter the cell's nucleus, where it can phosphorylate and activate a variety of transcription factors. These transcription factors control gene expression and can lead to a variety of cellular responses, including cell growth, proliferation, differentiation, and survival.

The MAPK pathway is a crucial signaling mechanism in cells, and its disruption can lead to a variety of diseases such as PIL.

RASopathy and its Potential Connection to Adult-Onset PIL

RASopathies are a class of genetic syndromes caused by mutations in genes that encode components or regulators of the RAS-MAPK pathway. These syndromes include neurofibromatosis type 1, Noonan syndrome, Costello syndrome, and others. The RAS-MAPK pathway, as discussed earlier, plays a pivotal role in many cellular processes, including cell growth, proliferation, differentiation, and survival.

In the context of adult-onset PIL, the hypothesis is that a RASopathy disrupts the normal functioning of the lymphatic system. Particularly, a mosaic activating mutation in a RAS gene could lead to the constitutive activation of the RAS protein, which in turn perpetually activates the MAPK pathway, disrupting the differentiation of LECs and resulting in the dilation and malfunction of lymphatic vessels seen in PIL.

The LEC Differentiation Program and the Role of ERK Suppression

The LEC differentiation program is a critical process for the development and maintenance of the lymphatic system. It involves the transformation of progenitor cells into mature LECs, which are responsible for the formation and function of lymphatic vessels.

Within the LEC differentiation program, the suppression of ERK activity plays a crucial role. ERK, a protein kinase in the MAPK pathway, is typically activated to promote cell proliferation. However, for LECs to differentiate properly, ERK activity needs to be suppressed, allowing the cells to exit the cell cycle and adopt the characteristics of mature LECs.

The suppression of ERK activity is essential for the proper differentiation of LECs and the maintenance of lymphatic vessel structure and function.

Turning Off ERK Activation, MEK Inhibitors, and Potential Reversal of PIL

As previously discussed, ERK activation is a critical part of the MAPK pathway, playing a central role in cell proliferation. However, for differentiation to occur, such as in the process of LEC differentiation, ERK activation needs to be suppressed, or "turned off".

The persistent activation of ERK due to a constitutively active RAS protein, as proposed in the case of a RAS mutation, disrupts the normal balance of proliferation and differentiation. This leads to the lymphatic vessel abnormalities seen in PIL.

Turning off this perpetual ERK activation allows the cells to exit the cycle of proliferation and enter the differentiation process. This allows the lymphatic vessels to regain normal function, reversing the symptoms of PIL.

MEK Inhibitors: MEK inhibitors are a class of drugs that specifically target and inhibit the MEK protein, a key component of the MAPK pathway. By inhibiting MEK, these drugs effectively suppress the downstream activation of ERK, essentially "turning off" the signal for cell proliferation.

Reversal of PIL: Using a MEK inhibitor in individuals with a RAS mutation causing PIL helps restore the normal balance of proliferation and differentiation in LECs. By inhibiting MEK, the perpetual activation of ERK caused by the RAS mutation is suppressed, allowing the cells to exit the cycle of proliferation and commence differentiation.

This allows the lymphatic vessels to regain their normal structure and function, thus reversing the dilation and malfunction seen in PIL. However, it's important to note that this is a theoretical proposition based on my current understanding of the MAPK pathway, RAS mutations, and MEK inhibitors.


In conclusion, adult-onset PIL is a rare medical condition characterized by the dilation of lymphatic vessels in the small intestine. While typically diagnosed in infancy or early childhood, adult-onset PIL can also occur, presenting with symptoms such weight loss, chronic diarrhea, and malabsorption.

Current treatments for PIL primarily involve dietary management, but they are often ineffective in adult cases. Alternative therapies such as Octreotide, Sirolimus, or antiplasmin may provide relief for some patients, but their effectiveness varies.

Through personal experience and research, I hypothesized that dysregulation of the MAPK signaling pathway, specifically through mosaic activating RAS mutations, may be responsible for some cases of adult-onset PIL. This dysregulation disrupts the normal differentiation of lymphatic endothelial cells, leading to the dilation and malfunction of lymphatic vessels seen in PIL. Thus, when a MEK inhibitor is taken, LEC differentiation occurs and lymphangiectasia is reversed, which is what I believe happened in my case.

Explain It Like I'm 5:

Imagine tiny pipes in our body called lymphatic vessels that help carry a special watery substance called lymph. These pipes should be working properly, but sometimes they become big and swollen like balloons. When this happens, it can cause problems in our belly like losing weight, having a tummy ache, or not being able to absorb the food we eat.

Doctors have different ways to help people with this problem. They might tell you to eat special foods or give you some special medicines to make the swollen pipes go back to their normal size. But sometimes, these treatments don't work very well for grown-ups.

I studied this problem and came up with an idea to explain why it happens. I think that there is a special pathway in our body that helps control the size of the pipes. But sometimes, this pathway gets mixed up, like when you put a puzzle piece in the wrong spot. When that happens, the pipes become too big and cause problems.

I also think that there might be some special medicines that can help put the puzzle piece in the right spot. These medicines can make the pipes go back to their normal size and make people feel better and when I took a MEK inhibitor that is what happened to me.


The information provided on this website,, is intended for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment.

While the author of this website has been diagnosed with adult-onset Primary Intestinal Lymphangiectasia and has shared personal theories and treatments that have worked for him, this should not be construed as medical advice. Your health situation may be different and the information provided here may not be applicable to your condition. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

The author and the website do not claim to offer definitive medical knowledge. Rather, they aim to share personal experiences and insights that might be helpful to others. The effectiveness of any treatment protocol will vary from person to person, and no specific results can be guaranteed.