Differentials
Herpes simplex virus infection
SIGNS / SYMPTOMS
Does not show the relapsing/remitting pattern of mental lucidity seen in rabies.
INVESTIGATIONS
HSV is detected in CSF by PCR with >95% sensitivity.
Enterovirus meningoencephalitis
SIGNS / SYMPTOMS
May show similar profound dysautonomia with cardiomyopathy.
INVESTIGATIONS
Enteroviruses are detected in CSF by PCR with >95% sensitivity.
West Nile virus encephalitis
SIGNS / SYMPTOMS
History of a mosquito bite.
Generally shows more parkinsonian findings or general body rigidity than rabies.
INVESTIGATIONS
West Nile virus-specific IgM in CSF is diagnostic.
Other arbovirus encephalitides
SIGNS / SYMPTOMS
History of a mosquito bite.
Generally show more parkinsonian findings or general body rigidity than rabies.
INVESTIGATIONS
Serum anti-arboviral antibodies are positive.
Rocky Mountain spotted fever and rickettsial encephalitis
SIGNS / SYMPTOMS
Petechial rashes or eschars are present.
INVESTIGATIONS
WBC count usually low.
Rocky Mountain spotted fever and other rickettsial serologies are diagnostic.
Japanese encephalitis
SIGNS / SYMPTOMS
Parkinsonian symptoms are common.
Patients develop hyperreflexia.
INVESTIGATIONS
Presence of Japanese encephalitis virus RNA in tissue, blood, or CSF is diagnostic.
Japanese encephalitis virus antibodies may be detected in CSF or serum.
Zika virus infection
SIGNS / SYMPTOMS
Mental status alterations, progression to coma. Guillain-Barre syndrome is strongly associated.
INVESTIGATIONS
RT-PCR testing in serum, CSF, or urine positive for Zika virus; serology positive for Zika virus antibodies
Guillain-Barre syndrome
SIGNS / SYMPTOMS
Acute flaccid paralysis is similar to paralysis seen in rabies, especially paralytic rabies.
Sphincter involvement is rare.
There is no fever.
INVESTIGATIONS
CSF shows elevated protein with a normal cell count (albuminocytologic dissociation).
Nerve conduction studies show slowing of nerve conduction velocities.
Limbic encephalitis
SIGNS / SYMPTOMS
Features are very similar to rabies. Seizures are common with limbic encephalitis with N-methyl-D-aspartate glutamate receptor (NMDAR) antibodies.
INVESTIGATIONS
Serum or CSF antibodies to N-methyl-D-aspartate (NMDA) glutamate receptor may be positive. Repeat testing may be needed.
Acute disseminated encephalitis
SIGNS / SYMPTOMS
Aerophobia and hydrophobia are absent, but other clinical features are similar to rabies.
INVESTIGATIONS
Brain MRI shows white matter lesions.
Tetanus
SIGNS / SYMPTOMS
Aerophobia, hydrophobia, and mental state changes are absent.
The main sign is trismus (which results in a grimace described as "risus sardonicus" or sardonic smile) associated with muscle rigidity, spasms, respiratory embarrassment, dysphagia, or autonomic dysfunction.
INVESTIGATIONS
Detection of tetanus toxin in plasma or clostridial culture from wound swab.
CSF is normal.
Bartonella encephalitis
SIGNS / SYMPTOMS
Associated with lymphadenitis.
INVESTIGATIONS
Bartonella serologies are diagnostic.
Delirium tremens
SIGNS / SYMPTOMS
History of chronic alcohol use and either reduction or cessation of drinking before presentation.
Prodromal illness is absent.
Fever is rare.
INVESTIGATIONS
The diagnosis is clinical.
Cocaine overdose
SIGNS / SYMPTOMS
History of cocaine use.
INVESTIGATIONS
Cocaine may be detected in urine, blood, or gastric contents. The half-life in blood is short.
Amphetamine overdose
SIGNS / SYMPTOMS
History of amphetamine abuse.
INVESTIGATIONS
Urine is positive for amphetamines.
Acute psychosis
SIGNS / SYMPTOMS
Main symptoms are hallucinations, delusions, and thought disorder, possibly accompanied by agitation. The prodrome and physical manifestations of rabies are absent.
Other clinical features depend on the cause.
INVESTIGATIONS
No differentiating tests.
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