A 63-year-old patient was initially presented to neurology services in 2010, complaining of ‘shakiness’ in his legs when standing for prolonged periods. His medical history included previous pulmonary sarcoidosis, seronegative arthropathy and a total hip replacement. There was no family history and he drank alcohol in moderate amounts, which had no effect on his symptoms.
Neurological examination was normal. Investigations were normal. No diagnosis was made at this time and he was discharged. In 2012, the patient developed a severe community-acquired pneumonia. He continued to complain of shakiness in his legs, and this worsened after admission. He described a sensation of shakiness and unsteadiness shortly after standing, which disappeared as soon as he sat down or started walking. There was no evidence of Parkinsonism or peripheral neuropathy. On the basis of the history, the patient was diagnosed with orthostatic tremor (OT).
OT is a rare condition characterised by a profound sense of unsteadiness when standing still, that is relieved by sitting or walking.¹ Despite the name, patients rarely complain specifically of tremor. While it is essentially a clinical diagnosis, it may be confirmed if the patient demonstrates a 13-18Hz high frequency tremor on EMG.¹
The prevalence and pathophysiology of the disorder are unknown.² Initial case series suggested the condition was non-progressive, although more recent reports have demonstrated that the majority of sufferers become increasingly disabled.³
In 1998, the International Parkinson and Movement Disorder Society defined OT as:¹,⁷
• A subjective feeling of unsteadiness during stance, but only in severe cases during gait, that is not present on sitting or lying down.
• Sparse clinical findings, mostly limited to a fine rippling of the leg muscles that may be easier to feel than see.⁴
The incidence and prevalence of OT is unknown.² However, OT is generally considered a rare disorder that is under-recognised and under-diagnosed.²,³ A 41-patient case series published in 2004 described a female predominance ratio of 2:1, with a mean age of onset of 64 years.² A significant diagnostic delay was reported, with a median of 5.7 years from symptom onset.² Overall, OT is considered an idiopathic condition as a family history is absent in most cases,²,³ although there have been a few case reports of OT occurring in siblings. ⁸,⁹,¹⁰
The most prominent presenting symptom is a subjective feeling of unsteadiness that improves on walking. Many compensate by adopting a wide-based stance and clawing the ground with their toes.⁷ Patients seek relief by sitting or leaning against something, and rarely fall or suffer injuries despite the sense of imbalance.¹ These symptoms result in a growing apprehension – and avoidance – of occupational or daily activities that involve prolonged standing such as queueing, significantly impacting on their quality of life.²
Auscultation of the gastrocnemius muscles when the patient is standing may identify a repetitive thumping sound named the ‘helicopter sign’.⁴,⁷
OT can be associated with a postural tremor in the upper limbs, as identified by Gerschlager in their case series.² Of those patients studied, 75% were described as having ‘primary OT’, with this cohort further divided into those with pure OT, and those with OT and arm tremor. Some have suggested that the arm tremor is ‘spread’ of the tremor from the legs.¹¹ The remaining 25% were described as ‘OT plus’, as the tremor was associated with additional neurological features including Parkinson’s disease, restless legs syndrome, aqueduct stenosis, dyskinesias, progressive supranuclear palsy (PSP), pontine lesions, head injury and cerebellar degeneration.² ,¹²
This diagnosis can be confirmed only by EMG recordings of a 13-18Hz tremor in the leg muscles on standing. All leg, trunk, and even arm muscles can show this tremor, which is typically absent during tonic activation while the patient is sitting or lying.⁷
Routine diagnostic tests, including blood tests, structural and functional imaging of the central nervous system, standard nerve conduction studies and EMG, are usually normal.⁷
Given the unusual nature of the symptoms, OT may be misdiagnosed as a functional disorder.⁴ Other common misdiagnoses include Parkinson’s disease, orthostatic myoclonus and restless legs syndrome.²,³
Given that some of these can occur as part of an ‘OT plus’ syndrome, they are not always unreasonable suggestions. However, careful history and examination should identify the characteristic features of OT, and alert the clinician to the diagnosis.
How can GPs diagnose it with certainty?
As with many neurological conditions, the diagnosis predominantly lies in the history. Unsteadiness when standing that improves when walking or sitting should raise suspicion of OT, even in the presence of other neurological features that may be clouding the clinical picture. Remember to look at the patient’s legs while they are standing, and listen for the helicopter sign.
A number of medications are suggested for symptomatic relief of OT, although the evidence is largely anecdotal, and the results are often disappointing.⁷ Clonazepam has been suggested as
a first-line treatment, with 30% describing an initial benefit, and this was maintained in the majority of patients mentioned in one case series.³ Another study reported primidone to be the most useful, with 26% reporting symptomatic improvement.¹⁴ Other second-line treatments include gabapentin, levodopa, phenobarbitone, pramipexole, and pregabalin, all either as a monotherapy or in combination.¹²,¹⁵
Overall, there is a lack of good quality data to guide clinicians on the treatment of OT. The general advice is to adopt a trial-and-error approach to management, with the recommendation that clonazepam and gabapentin are probably the best initial treatments.¹²,¹⁵ However, the response to medication is frequently unsatisfactory, with many patients being refractory to treatment.¹²
Physical aids such as portable stools may provide symptomatic relief.⁷ Weight reduction in obese individuals may also be beneficial.⁷
When to refer
The diagnosis of OT can be challenging, particularly if there are additional neurological features that may complicate the clinical picture and cause concern about an alternative diagnosis. Referral or discussion with neurology services is appropriate in most cases.
Dr Richard Davenport is a consultant neurologist for the department of clinical neurosciences at Western General Hospital in Edinburgh
Dr Louise Davidson is a research registrar for the National CJD Research and Surveillance Unit at Western General Hospital in Edinburgh
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