The syndrome can be difficult to diagnose and may be misdiagnosed as autism, pervasive developmental disorder, hearing impairment, learning disability, auditory/verbal processing disorder, attention deficit hyperactivity disorder, intellectual disability, childhood schizophrenia, or emotional/behavioral problems. An EEG (electroencephalogram) test is imperative to a diagnosis. Many cases of patients exhibiting LKS will show abnormal electrical brain activity in both the right and left hemispheres of the brain; this is exhibited frequently during sleep. Even though an abnormal EEG reading is common in LKS patients, a relationship has not been identified between EEG abnormalities and the presence and intensity of language problems. In many cases however, abnormalities in the EEG test has preceded language deterioration and improvement in the EEG tracing has preceded language improvement (this occurs in about half of all affected children). Many factors inhibit the reliability of the EEG data: neurologic deficits do not closely follow the maximal EEG changes in time. The most effective way of confirming LKS is by obtaining overnight sleep EEGs, including EEGs in all stages of sleep. Many conditions like demyelination and brain tumors can be ruled out by using magnetic resonance imaging (MRI). In LKS, fluorodeoxyglucose (FDG) and positron emission tomography (PET) scanning can show decreased metabolism in one or both temporal lobes - hypermetabolism has been seen in patients with acquired epileptic aphasia. Most cases of LKS do not have a known cause. Occasionally, the condition may be induced secondary to other diagnoses such as low-grade brain tumors, closed-head injury, neurocysticercosis, and demyelinating disease. Central Nervous System vasculitis may be associated with this condition as well. Differential diagnosis The table below demonstrates the extensive and differential diagnosis of acquired epileptic aphasia along with Cognitive and Behavioral Regression: Diagnosis Deterioration EEG Patterns Autistic epileptiform regression Expressive language, RL, S, verbal and nonverbal communication Centrotemporal spikes Autistic regression Expressive language, RL, S, verbal and nonverbal communication Normal Acquired epileptic aphasia RL, possibly behavioral Left or right temporal or parietal spikes, possibly ESES Acquired expressive epileptic aphasia Expressive language, oromotor apraxia Centrotemporal spikes (ESES) Expressive language, RL, possibly behavioral ESES Developmental dysphasia (developmental expressive language disease) No; lack of expressive language acquisition Temporal or parietal spikes Disintegrative epileptiform disorder Expressive language, RL, S, verbal and nonverbal communication, possibly behavioral ESES Stuttering Expressive language, no verbal-auditory agnosia Spike-and-wave discharges on the left temporocentral and frontal regions Note: EEG = electroencephalographic; ESES = electrical status epilepticus of sleep; RL = receptive language; S = sociability * Continuous spike and wave of slow-wave sleep (>85% of slow-wave sleep).
Landau–Kleffner syndrome
Smith–Lemli–Opitz syndrome
Letterer–Siwe disease
Kapur–Toriello syndrome
Klüver–Bucy syndrome
Smith–Magenis syndrome
Pelger–Huët anomaly
Schinzel–Giedion syndrome