The earliest and most common symptom of ankylosing spondylitis is a deep, dull pain in the lower back and buttocks that develops gradually, typically in late adolescence or early adulthood. Unlike back pain from a muscle strain or herniated disc, this pain feels worse after rest, is often at its peak in the morning or during the night, and improves with movement and exercise. That pattern of “better with activity, worse with stillness” is the hallmark that distinguishes it from mechanical back pain.
Because the disease develops slowly and back pain is so common, the average time from first symptoms to diagnosis is about 7 years, a delay that hasn’t improved much in decades. Knowing what to look for can help you recognize the condition earlier and get treatment before the disease progresses.
Inflammatory Back Pain and Stiffness
The back pain of ankylosing spondylitis starts in the sacroiliac joints, the two joints where your spine meets your pelvis. You might feel it deep in your lower back or in your buttocks, sometimes on one side, sometimes both. Early on, it’s easy to dismiss as a pulled muscle or the result of sitting too long at a desk.
What sets this pain apart is its behavior. It tends to wake you during the second half of the night. Morning stiffness can last 30 minutes or more and loosens up once you start moving around. Sitting still for long stretches, like a long car ride or a movie, makes it flare. Exercise and stretching bring relief, which is the opposite of what happens with most structural back injuries. This combination of features is what doctors refer to as “inflammatory” back pain, and it reflects the underlying immune-driven inflammation rather than physical damage to a disc or muscle.
Pain Beyond the Spine
Ankylosing spondylitis doesn’t stay limited to the back in many people. Inflammation can target the entheses, the spots where tendons and ligaments attach to bone. This is called enthesitis, and it produces pain, stiffness, and sometimes swelling at those connection points. Common locations include the heel (where the Achilles tendon meets the bone), the bottom of the foot (similar to plantar fasciitis), the knees, elbows, and shoulders. The pain is often worst when you first put weight on the area after resting.
Some people also develop peripheral arthritis, meaning swelling and pain in joints outside the spine, such as the hips, knees, or ankles. Hip involvement is particularly significant because it can limit walking and is one of the factors associated with more severe disease over time.
How Symptoms Differ in Women
Ankylosing spondylitis has historically been considered a disease that mainly affects men, but that reputation is partly the result of how it’s detected. Women with the condition tend to have less visible damage on X-rays, both in the sacroiliac joints and along the spine. That lower rate of radiographic change means the disease is more likely to be missed or diagnosed later in women.
At the same time, women tend to report more pain, greater fatigue, and higher overall disease activity than men. They’re also more likely to experience peripheral symptoms like enthesitis and joint swelling in the arms and legs rather than purely spinal involvement. Some of the increased pain burden in women may be related to central sensitization, a process in which the nervous system amplifies pain signals, causing pain even in areas without active inflammation. The takeaway is that a woman with widespread pain and stiffness shouldn’t rule out ankylosing spondylitis just because her back X-ray looks normal.
Eye, Skin, and Gut Involvement
Ankylosing spondylitis is a systemic inflammatory disease, which means it can affect organs beyond the joints. The most common extra-articular symptom is acute anterior uveitis, an inflammation inside the eye. It causes sudden eye pain, redness, sensitivity to light, and blurred vision, usually in one eye at a time. About 11% of patients already have it at the time of their AS diagnosis, and over 20 years, roughly one in four will experience at least one episode. It requires prompt treatment to prevent lasting vision damage, so any sudden eye pain or light sensitivity is worth taking seriously.
Psoriasis, a condition causing red, scaly skin patches, occurs in about 4% of patients at diagnosis and reaches roughly 10% over two decades. Inflammatory bowel disease, which causes chronic digestive symptoms like abdominal pain, diarrhea, and bloody stools, affects about 4% at diagnosis and around 7.5% over 20 years. These aren’t coincidences. They share overlapping immune pathways with ankylosing spondylitis, and their presence can actually help confirm the diagnosis.
Fatigue and Sleep Disruption
Fatigue is one of the most underappreciated symptoms of ankylosing spondylitis. It’s not ordinary tiredness from a busy day. It’s a deep, persistent exhaustion that doesn’t fully resolve with sleep. In studies of patients with early-stage disease, about 45% report significant sleep disturbances. Nocturnal back pain, particularly related to sacroiliac joint tenderness, is a direct contributor. The pain disrupts deep sleep and makes it difficult to stay asleep through the night, creating a cycle where poor sleep increases pain sensitivity and inflammation, which in turn worsens sleep.
Fatigue and sleep problems are closely linked to overall disease activity. When inflammation is more active, energy drops further. Many patients find that fatigue affects their daily life as much as, or more than, the pain itself.
Reduced Chest Expansion and Breathing
As inflammation spreads to the joints between the ribs and the spine, the rib cage can gradually lose flexibility. You might notice it first as a feeling of tightness across the chest when you try to take a deep breath. In clinical settings, chest expansion below 2.5 centimeters (measured at the nipple line during a full inhale) is considered restricted, though this measurement is more useful for tracking progression than for initial diagnosis. Over time, reduced chest mobility can make deep breathing harder and leave you relying more on your diaphragm, which can contribute to feelings of breathlessness during exertion.
What Advanced Disease Looks Like
Without treatment, ankylosing spondylitis can progress over years or decades to the point where the vertebrae of the spine begin to fuse together. The ligaments and discs between the vertebrae calcify, and new bone growth bridges the gaps between spinal bones. On X-ray, this creates a characteristic “bamboo spine” appearance.
Paradoxically, once the spine is fully fused, the chronic back pain often decreases or disappears. But mobility goes with it. A fused spine is rigid, making it impossible to bend or twist normally. In some cases, the spine fuses in a forward-stooped position, making it difficult to stand upright or look straight ahead. The fused vertebrae also become brittle, making them significantly more vulnerable to fractures from even minor trauma. If pain suddenly returns after a long pain-free period in someone with a fused spine, a fracture is a real concern.
It’s worth noting that modern treatments have made full spinal fusion far less common than it once was. Early diagnosis and consistent treatment can slow or prevent this progression in most people.
The Role of Genetics
About 85% of people with ankylosing spondylitis carry a gene called HLA-B27. If you have a family member with AS and you’re experiencing inflammatory back symptoms, this genetic marker can be a useful piece of the diagnostic puzzle. However, carrying the gene doesn’t mean you’ll develop the disease. HLA-B27 is present in about 6 to 8% of the general population, and most of those people never develop ankylosing spondylitis. It increases risk but doesn’t determine outcome.
Diagnosis relies on the full picture: the pattern of symptoms, blood markers of inflammation, imaging of the sacroiliac joints (often with MRI, which can detect inflammation before X-ray changes appear), and the presence or absence of HLA-B27. No single test confirms it on its own, which is part of why that 7-year diagnostic delay persists.