Leg pain is a frequent complaint in physio clinics. All too often it’s brushed off as “sciatica”, but the poor sciatic nerve isn’t always the culprit. Leg pain can have somatic, neuropathic, vascular and systemic causes, which makes assessment complex to say the least! Identifying the correct cause of pain is important, as every diagnosis requires a different treatment approach. This blog will cover some of the main differential diagnoses of leg pain and how to recognize them, so next time someone comes to your clinic complaining of leg pain, you’ll know better than to simply label it sciatica.

Somatic drivers

Low back

As many as 60% of people with leg pain also complain of low back issues. But knowing which structure might be responsible for the leg pain isn’t so simple. Nerve roots, discs, facet joints, the SI joint… They can all cause pain in the legs! Treatment depends on whether the pain is somatic or neuropathic, which is why one of the first questions to answer is whether the leg pain is referred or radicular. Luckily, each comes with their own specific pain experience. Referred pain is typically diffuse, dull and achy. It usually follows a mechanical pattern and pain is often much worse in the back than it is in the leg. On the other hand, radicular pain is much more localized and, contrary to popular belief, doesn’t always follow dermatomes (only one third of cases do!). Patients complain of shooting, burning pains which are capricious, and aren’t necessarily provoked by specific activities or movements. The leg pain is usually more bothersome than the back, and neurodynamic testing will most likely be positive.

Hip osteoarthritis (OA)

Pain caused by hip OA is often felt in the greater trochanteric, groin or buttock region, but can refer more distally (even below the knee). The fact that hip and low back pain have overlapping symptoms makes for a tricky differential diagnosis. Additionally, hip and low back pain are often concomitant, which makes it even more complex. However, if your patient is limping, they are 7x more likely to experience hip than back problems. Groin pain is 7x more likely to come from the hip than the back, and if there’s an additional internal rotation deficit, chances are even higher that the hip is the main culprit! Some of the more functional features include pain that is worse in the first 30 minutes of the day, catching/clicking sensations, instability, and pain with putting on socks/shoes and getting in/out of the car.

Greater Trochanteric Pain Syndrome (GTPS)

This will often cause referred pain in the lateral leg. It affects females more than males and there appears to be a correlation with chronic low back pain, as up to 45% of people with GTPS also complain of low back symptoms. GTPS often arises after a change in load/activity and elicits pain with side lying, cross-legged sitting and ascending/descending stairs. Recent findings suggest there might be a connection between GTPS and decreased estrogen levels, which could explain why females during and after menopause are more prone to suffer from the condition.

Deep Gluteal Syndrome (DGS)

You might know this one better as Piriformis Syndrome. DGS is a non-discogenic entrapment of the sciatic nerve within the subgluteal space, which is basically an umbrella term whereby a multitude of different structures can create many vague symptoms in this area. PGS will typically cause buttock and retro-trochanteric pain which is provoked by sitting, palpation of the buttock, and passive and resisted hip movements.

Neuropathic causes

Sciatica

Sciatica is the first thing a lot of people think about when experiencing leg pain. It isn’t as common as we think though, with only 2-3% of the population in the UK being diagnosed each year. However, it’s important to guide people with sciatica appropriately, as they typically experience worse pain, and have higher risk of poor outcomes. What makes sciatica so difficult is its heterogeneity – you may have already noticed from experience that no person with sciatica has the exact same symptoms. What’s most important is recognizing the general symptoms of radicular pain we’ve already described above: leg pain worse than back pain, usually distal to the knee, with objective neurological findings and neuropathic pain qualities. Unfortunately, the dermatomes we’ve so carefully studied in school aren’t always very accurate when it comes to this condition – things like thermal or mechanical hyperalgesia and sensory loss may affect some but definitely not all people with sciatica. Pain is most typically felt in the calf, then foot and lastly knee/thigh region. One of the key messages to give people with sciatica is that it needs time; 90% of people are thought to improve within 4 months, but one third of people continue to have symptoms after a year.