Study finds 4-month diagnostic gap between key ALS types

People whose amyotrophic lateral sclerosis (ALS) begins with speech and swallowing problems, known as bulbar onset, are typically diagnosed about four months sooner than those whose disease begins with arm or leg weakness, known as limb onset.

That’s according to a pooled analysis of data from 13 studies across eight countries and more than 3,300 patients. The researchers noted that, while the earlier diagnosis of bulbar onset is real, the precise timing remains uncertain.

“Strategies raising awareness of limb-onset ALS among primary care and orthopedic physicians are warranted,” the authors wrote in the study, “Diagnostic Delay in Amyotrophic Lateral Sclerosis: A Systematic Review and Meta-Analysis Comparing Time From Symptom Onset to Diagnosis in Bulbar-Onset Versus Limb-Onset Disease,” published in Cureus.

In people with ALS, the nerve cells that control muscle movement, called motor neurons, gradually die. This leads to progressive muscle weakness, and most people survive two to four years after ALS symptoms first appear.

ALS can begin in different parts of the body. Limb-onset disease, which starts with weakness in an arm or leg, makes up roughly 60% to 70% of cases. Bulbar-onset disease, which starts with slurred speech, trouble swallowing, or voice changes, accounts for about 25% to 30% of cases.

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Scientists pool data to look for answers

There is no definitive test to confirm ALS. Instead, doctors rely on clinical criteria that look for evidence of damage to both the upper motor neurons (brain to spinal cord) and lower motor neurons (spinal cord to muscles), and often need to observe the disease over time before making a formal ALS diagnosis.

Because of this, the interval between symptom onset and a confirmed diagnosis has generally been reported to be between nine and 18 months. While individual research groups have reported this delay separately for bulbar-onset and limb-onset disease, no one had combined the estimates into a single pooled comparison.

To address this gap, scientists searched two medical databases and identified 13 eligible studies published between 2000 and 2023. These studies involved 898 patients with bulbar onset and 2,438 patients with limb onset. Nine of the studies provided enough statistical data to be pooled for analysis, while the remaining four were described narratively.

In the pooled analysis, bulbar-onset patients were diagnosed a mean of 4.42 months faster than limb-onset patients. All pooled studies, as well as all four narrative studies, pointed in the same direction, favoring earlier diagnosis in bulbar-onset disease.

A statistical test that removed one study at a time showed the result remained consistent, ranging from 4.08 to 4.74 months, indicating no single study was driving the findings.

The researchers suggested the gap may relate to how bulbar symptoms are recognized as ALS and how alarming those symptoms are to patients and doctors. As the authors describe it, bulbar symptoms are “unusual, distressing, and obvious,” which may prompt faster referral to a neurologist.

Limb weakness, by contrast, is common and often initially attributed to more familiar conditions such as spinal disease, carpal tunnel syndrome, or peripheral neuropathy (nerve damage outside the brain and spinal cord). As a result, patients may see other specialists before reaching a neurologist.

The researchers noted some limitations in their analysis, including that most of the studies were retrospective and relied on patients or clinicians to recall when symptoms began. This can introduce inaccuracies.

Using a formal grading system called GRADE, the certainty of the overall evidence was rated as very low, mainly because the included studies were retrospective. The authors said this rating reflects uncertainty in the exact size of the four-month gap, rather than its direction.

But because ALS survival is measured in months, this diagnostic gap is clinically meaningful, “because it postpones disease-modifying treatment and multidisciplinary care,” they said.

“The results support targeted awareness strategies directed at the clinicians most likely to encounter limb-onset presentations, including primary care physicians, orthopedic surgeons, and spine specialists, to reduce diagnostic delay and maximize the therapeutic window for available treatments,” the team concluded.