A drop attack is a sudden fall, with or without unconsciousness, due either to collapse of muscle tone or abnormal muscle contraction in the legs. Many neurological diseases, cardiac diseases, ear diseases, muscle dysfunction conditions like myoclonic syndromes and startle responses can cause drop attacks. In about 30% of drop attacks the cause is unknown.
Weakness of muscles of the legs
Weakness of the hip and knee extensor muscles (important for maintaining an erect posture)
Some causes include muscular dystrophy, neurogenic atrophy, polymyositis, myasthenia gravis and spinal cord ischemic attacks. Duchenne’s muscular dystrophy is the most common cause of muscle dystrophy.
Isolated quadriceps weakness – secondary to diseases like polymyositis, inclusion body myositis and neurogenic atrophy, and the legs may suddenly give way without warning to cause falls
Intermittent spinal ischemia can produce sudden attacks of transient paraparesis or falls, and causes include syphilitic arteritis, arteriosclerosis of the distal aorta, adhesive arcachnoiditis, spinal compression due to spinal stenosis or disc herniation; the attacks are often precipitated by exercise and relieved by rest
Patients with Parkinson’s disease often fall due to defective postural reflexes, sudden freezing, and uncoordinated turning; their stooped flexed posture predisposes them to falling forward because their centre of gravity is displaced forward when standing or walking.
Other neurodegenerative diseases associated with frequent falls include progressive supranuclear palsy, corticobasal degeneration, Huntington’s chorea, multiple system atrophy and Alzheimer’s disease
Transient ischemic attacks
A patient with vertebro-basilar artery ischemia can present with a sudden loss of tone in their legs, causing their knees to buckle. The patient falls powerlessly without protective arm movements; There may be no precipitating head or neck movements or loss of consciousness, The patient can get up and walk immediately or within one minute. Usually other symptoms of brainstem ischemia are present (vertigo, diplopia, blurred vision, sensory changes, motor weakness, which suggest the diagnosis.
Drop attacks can be due to sudden muscle contractions associated with generalized convulsive epilepsy, or a sudden loss of postural tone due to atonic epilepsy or epileptic negative myoclonus.
Atonic epileptic attacks in children can occur when standing or sitting or lying, and there is no aura or state of confusion; sudden drop attacks can cause the patient to collapse with triple flexion of the legs and no involvement of the arms. The patient can usually get up immediately after an attack.
Various myoclonic syndromes
Mycoclonus is a sudden brief, shock-like muscle movement caused by a brief muscle contraction (positive myoclonus) or inhibition of a muscle contraction (negative myoclonus)
It can mimic idiopathic drop attacks, and the patient can fall suddenly with buckling of the legs
Pathological startle reactions (hypereflexia) are characterized by an exaggerated motor response to unexpected auditory stimuli, and less frequently to visual or somasthetic stimuli.
They consist of both brief myoclonic jerks and longer tonic spasms
Hypereflexia may have a variety of causes eg. idiopathic, hereditary, or secondary to acquired brainstem diseases – post-anoxic encephalopathy, viral or paraneoplastic brainstem encephalitis, multiple sclerosis, sarcoidosis or brainstem strokes. Myoclonic jerks occur frequently during the day, but also at night when the patient is asleep, and mainly affect the legs
Sterotyped tonic spasms consist of facial grimacing, flexion of the neck and trunk, flexion or extension of the hips and knees, and characteristic abduction of the shoulders with flexion of the elbows. The patient falls forwards rigidly like a log, but sometimes falls backwards; protective reflexes are impossible and injuries common; consciousness is maintained during the fall and recovery is fast
Cataplexy and paroxysmal choreoathetosis
Cataplexy can cause sudden falls without LOC, but the patient cannot speak during the fall
Characteristic precipitating factors include laughter or a sudden emotional stimulus. Minor symptoms of cataplexy may consist of a brief drop of the jaw and sagging of the head, but severe attacks can cause loss of tone in all the antigravity muscles and the patient falls powerlessly and loosely and remains immobile for many seconds (longer than in hypereflexia)
Paroxysmal choreoathetosis – attacks are usually precipitated by sudden leg movements during standing or running or social embarrassment => the patient may suddenly lose control due to tonic spasms or an involuntary choreoathetotic muscle movement and fall like a log
Posterior cranial fossa pathology
Mass lesions around the foramen magnum can cause drop attacks
Odontoid process fractures
Arnold-Chiari type I malformations
Drop attacks can be precipitated by neck movements, coughing or sneezing, or vertical head compression;
the drop attack patient presents with a stiff neck, spastic paraplegia and limb paresthesias
Posterior fossa arachnoid cysts, midline metastatic cerebellar tumors, vermis hemangioblastomas, and obstructive hydrocephalus due to third ventricle cysts
Meniere’s drop attacks (Tumarkin’s otolithic crisis)
Seen in the early or late stages of Meniere’s disease when there is a sudden change in endolymphatic pressure which causes end-organ stimulation with a reflex-like vestibulospinal loss of postural tone. The patient suddenly loses control of balance and falls and he sometimes with a distinct feeling of being pushed or thrown to the ground. The patient does not lose consciousness.
(* a patient with Wallenberg’s syndrome, due to a lateral medullary stroke, may have a similar transient sensation of being pulled or pushed to the side, and the patient suddenly falls to the side without realizing that it is his active shift of the centre of gravity – lateropulsion – that causes the momentary imbalance)
Idiopathic drop attacks (no specific cause found)
A fall without warning, not associated with loss of consciousness, not apparently due to any malfunction of the legs, not induced by changes of posture or movement of the head, and not accompanied by vertigo or other cephalic sensation, and not associated with myoclonic jerks
It usually appears between the ages 40 – 60 years. Patients only fall when standing or walking, and they usually buckle at the knees and fall forwards.
The attacks occur very suddenly and the patient cannot remember if he lost consciousness, or not; the patient can get up immediately unless accidental injury occurs (minor upper limb fractures and/or dislocations are common in the elderly)
Serial attacks are rare, and spontaneous remission is common (25 – 80%)