Fat-soluble vitamin deficiency and toxicity: Pathology review

At the clinic, 32 year old Naya comes in with bilateral hip pain. She exercises regularly and has not changed anything in her routine recently. She mentions that she has recently also started to experience blurry vision, and has scheduled an appointment with her ophthalmologist. In addition, she mentions that her skin is unusually dry, which hasn’t improved with moisturizing cream. She takes several tablets of cod liver oil supplements daily. Physical examination reveals an enlarged liver and spleen. Next to her, 2 year old Lorenzo has been brought to the clinic by his mother for a yearly pediatric checkup. He was diagnosed with chronic kidney disease about one year ago in Italy. They then migrated to the United Kingdom. On examination, there is lateral bowing of the legs, as well as beading of the ribs along the anterior side of the chest.

Based on the initial presentation, both Naya and Lorenzo seem to have some form of fat- soluble vitamin deficiency or toxicity. Fat- soluble vitamins include vitamins A, D, E, and K. Just like all vitamins, they need to be attained by diet. So, inadequate dietary consumption can be the cause of their deficiency. In a test question, some big clues are that the affected individuals often come from lower income countries or have an eating disorder like anorexia nervosa. Now, in the small intestine, fat- soluble vitamins are absorbed along with dietary fats, which means that anything affecting fat absorption can also affect the absorption of fat-soluble vitamins. Fat malabsorption typically presents with steatorrhea, meaning fatty, greasy, floating, voluminous, and terribly smelling stools. But a deficiency of fat-soluble vitamins might be the only clue you get for that. Now, causes of fat malabsorption can be broadly divided into two major groups: digestive disorders where the food can’t be broken down in the intestinal lumen, and absorption defects where the intestinal mucosa can’t take in the nutrients.

For your exams, the most common digestive disorders are exocrine pancreatic insufficiency and cholestasis. In exocrine pancreatic insufficiency, there’s a lack of pancreatic digestive enzymes, including lipase, which breaks down lipids. Now, what’s important to remember is that exocrine pancreatic insufficiency typically results from chronic pancreatitis, which is inflammation of the pancreas leading to the destruction of its exocrine portion. In adults, the greatest risk factor for chronic pancreatitis is alcohol abuse, whereas if you see chronic pancreatitis in a child, remember that the number one cause is cystic fibrosis. Fat digestion could also be affected by cholestasis, where not enough bile is reaching the intestine to emulsify fats and make them easier to absorb. Cholestasis can be hepatocellular, where hepatocytes don’t make enough bile, and commonly tested causes include increased estrogen like in pregnancy or oral contraceptive use. It could also be due to obstruction where something’s physically blocking bile flow. In a test question, think of obstructive cholestasis if you see a tumor in the head of the pancreas, primary sclerosing cholangitis, in an individual with a history of inflammatory bowel disease, or biliary atresia in a newborn.