What Are Splinter Hemorrhages?

These dark spots under your nails could be warning you.

You probably know by now that your nails can tell you much about your health. For example, some nail changes can be a warning sign of kidney and liver disease, while others may be an indication of skin problems. But did you know your nails can even signal health problems as serious as an infection of the heart valves?

A photo published in 2019 by the New England Journal of Medicine (NEJM) brought this to our attention. It features the hands of a 48-year-old male patient who had what are called splinter hemorrhages.

What Are Splinter Hemorrhages, Exactly?

Splinter hemorrhages get their name because they look like a splinter under the nail, according to MedlinePlus. They show up as small dark marks under a person's nail plates and run in the same direction the nail grows. These reddish-brown streaks are one to three millimeters long and do not fade or blanch when pressed.

They're more common for men and people with dark complexions. They usually occur in fingernails but can also appear in toenails.

A hemorrhage occurs when blood leaks from a ruptured blood vessel. At the tip of the fingers, it is the capillaries, the smallest blood vessels in the body, that rupture. "The blood attaches to the nail plate and moves distally as the nail grows," the American Academy of Family Physicians (AAFP) explained. (Distally means away from the center, so in the case of splinter hemorrhages, out toward the end of the fingernail or toenail.)

What Causes Splinter Hemorrhages?

Causes of splinter hemorrhages vary, ranging from external causes to serious health conditions. The AAFP names environmental factors, skin disorders (like psoriasis and eczema), systemic lupus erythematosus, and medication use as some of the things that can cause splinter hemorrhages. If splinter hemorrhages are accompanied by pain, this can indicate that a systemic disease, one that affects the whole body, is the culprit.

And these aren't the only conditions associated with splinter hemorrhages. According to a report from JAMA Dermatology, splinter hemorrhages can also be caused by hemodialysis (treatment for kidney disease), antiphospholipid syndrome (an immune-system problem that can increase the risk of blood clots), and vasculitis (inflammation of the blood vessels). In about 20% of cases, splinter hemorrhages are caused simply by nail trauma, according to the AAFP.

splinter-hemorrages
NEJM

However, the NEJM also reported that splinter hemorrhages could be a sign of a serious health problem—a condition called endocarditis, which is an infection in the heart chambers and valves. Endocarditis can occur if fungi, bacteria, or other germs enter your body (via your mouth or another opening) and spread to damaged parts of the heart.

If splinter hemorrhages are accompanied by other symptoms like fever, tender purple-pink spots usually found at the end of fingers and toes (Osler nodes), or non-tender discolored patches of skin on the palms or soles (Janeway lesions), make an appointment to get evaluated by a healthcare provider. Your healthcare provider may want to check for other signs of endocarditis by listening for a murmur and doing an eye exam to look for a hemorrhage in the retina, the back part of your eye. Any of these symptoms, in addition to splinter hemorrhages, can indicate endocarditis, according to the AAFP.

How Are Splinter Hemorrhages Treated?

Splinter hemorrhages can be temporary or long-term: If the blood attaches to the nail plate and not the nail bed, it'll grow out as the nail grows. But if they attach to the nail bed, the dark lines might remain stationary according to the AAFP.

Clinicians and researchers learned that the patient featured in the NEJM report had a type of endocarditis called nonbacterial thrombotic endocarditis. He also had pancreatic cancer, the report noted.

If you do notice splinter hemorrhages popping up under your fingernails after your nails have experienced trauma (think an injury from sports, housework, or personal habits), remember that the blood could simply be a natural consequence. When caused by trauma, splinter hemorrhages will occur only on the injured finger, thumb, or toe and do not require treatment because they will grow out naturally.

When due to systemic causes, splinter hemorrhages are more likely to affect multiple digits. If you haven't been in any recent accidents and you notice the lines, having a quick conversation with your healthcare provider could be worth it to make sure nothing else is going on with your body.

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