In adults, the most common symptom of meningitis is a severe headache, occurring in almost 90% of cases of bacterial meningitis, followed by nuchal rigidity (the inability to flex the neck forward passively due to increased neck muscle tone and stiffness). The classic triad of diagnostic signs consists of nuchal rigidity, sudden high fever, and altered mental status; however, all three features are present in only 44–46% of bacterial meningitis cases. If none of the three signs are present, acute meningitis is extremely unlikely. Other signs commonly associated with meningitis include photophobia (intolerance to bright light) and phonophobia (intolerance to loud noises). Small children often do not exhibit the aforementioned symptoms, and may only be irritable and look unwell. The fontanelle (the soft spot on the top of a baby's head) can bulge in infants aged up to 6 months. Other features that distinguish meningitis from less severe illnesses in young children are leg pain, cold extremities, and an abnormal skin color.

Nuchal rigidity occurs in 70% of bacterial meningitis in adults. Other signs include the presence of positive Kernig's sign or Brudziński sign. Kernig's sign is assessed with the person lying supine, with the hip and knee flexed to 90 degrees. In a person with a positive Kernig's sign, pain limits passive extension of the knee. A positive Brudzinski's sign occurs when flexion of the neck causes involuntary flexion of the knee and hip. Although Kernig's sign and Brudzinski's sign are both commonly used to screen for meningitis, the sensitivity of these tests is limited. They do, however, have very good specificity for meningitis: the signs rarely occur in other diseases. Another test, known as the "jolt accentuation maneuver" helps determine whether meningitis is present in those reporting fever and headache. A person is asked to rapidly rotate the head horizontally; if this does not make the headache worse, meningitis is unlikely.

Other problems can produce symptoms similar to those above, but from non-meningitic causes. This is called meningism or pseudomeningitis.

Meningitis caused by the bacterium "Neisseria meningitidis" (known as "meningococcal meningitis") can be differentiated from meningitis with other causes by a rapidly spreading petechial rash, which may precede other symptoms. The rash consists of numerous small, irregular purple or red spots ("petechiae") on the trunk, lower extremities, mucous membranes, conjuctiva, and (occasionally) the palms of the hands or soles of the feet. The rash is typically non-blanching; the redness does not disappear when pressed with a finger or a glass tumbler. Although this rash is not necessarily present in meningococcal meningitis, it is relatively specific for the disease; it does, however, occasionally occur in meningitis due to other bacteria. Other clues on the cause of meningitis may be the skin signs of hand, foot and mouth disease and genital herpes, both of which are associated with various forms of viral meningitis.

Additional problems may occur in the early stage of the illness. These may require specific treatment, and sometimes indicate severe illness or worse prognosis. The infection may trigger sepsis, a systemic inflammatory response syndrome of falling blood pressure, fast heart rate, high or abnormally low temperature, and rapid breathing. Very low blood pressure may occur at an early stage, especially but not exclusively in meningococcal meningitis; this may lead to insufficient blood supply to other organs. Disseminated intravascular coagulation, the excessive activation of blood clotting, may obstruct blood flow to organs and paradoxically increase the bleeding risk. Gangrene of limbs can occur in meningococcal disease. Severe meningococcal and pneumococcal infections may result in hemorrhaging of the adrenal glands, leading to Waterhouse-Friderichsen syndrome, which is often fatal.

The brain tissue may swell, pressure inside the skull may increase and the swollen brain may herniate through the skull base. This may be noticed by a decreasing level of consciousness, loss of the pupillary light reflex, and abnormal posturing. The inflammation of the brain tissue may also obstruct the normal flow of CSF around the brain (hydrocephalus). Seizures may occur for various reasons; in children, seizures are common in the early stages of meningitis (in 30% of cases) and do not necessarily indicate an underlying cause. Seizures may result from increased pressure and from areas of inflammation in the brain tissue. Focal seizures (seizures that involve one limb or part of the body), persistent seizures, late-onset seizures and those that are difficult to control with medication indicate a poorer long-term outcome.

Inflammation of the meninges may lead to abnormalities of the cranial nerves, a group of nerves arising from the brain stem that supply the head and neck area and which control, among other functions, eye movement, facial muscles, and hearing. Visual symptoms and hearing loss may persist after an episode of meningitis. Inflammation of the brain (encephalitis) or its blood vessels (cerebral vasculitis), as well as the formation of blood clots in the veins (cerebral venous thrombosis), may all lead to weakness, loss of sensation, or abnormal movement or function of the part of the body supplied by the affected area of the brain.

Fever and headache are the cardinal features, confusion is a late feature and coma bears a poor prognosis. Meningism is absent in a fifth of patients with TB meningitis. Patients may also have focal neurological deficits.

Viral meningitis characteristically presents with fever, headache and neck stiffness. Fever is the result of cytokines released that affect the thermoregulatory neurons of the hypothalamus. Cytokines and increased intracranial pressure stimulate nociceptors in the brain that lead to headaches. Neck stiffness is the result of inflamed meninges stretching due to flexion of the spine. In contrast to bacterial meningitis, symptoms are often less severe and do not progress as quickly. Nausea, vomiting and photophobia (light sensitivity) also commonly occur, as do general signs of a viral infection, such as muscle aches and malaise. Increased cranial pressure from viral meningitis stimulates the area postrema, which causes nausea and vomiting. Photophobia is due to meningeal irritation. In severe cases, people may experience concomitant encephalitis (meningoencephalitis), which is suggested by symptoms such as altered mental status, seizures or focal neurologic deficits.

Babies with viral meningitis may only appear irritable, sleepy or have trouble eating. In severe cases, people may experience concomitant encephalitis (meningoencephalitis), which is suggested by symptoms such as altered mental status, seizures or focal neurologic deficits. The pediatric population may show some additional signs and symptoms that include jaundice and bulging fontanelles.

Mycobacterium tuberculosis of the meninges is the cardinal feature and the inflammation is concentrated towards the base of the brain. When the inflammation is in the brain stem subarachnoid area, cranial nerve roots may be affected. The symptoms will mimic those of space-occupying lesions.

Blood-borne spread certainly occurs, presumably by crossing the blood–brain barrier; but a proportion of patients may get TB meningitis from rupture of a cortical focus in the brain; an even smaller proportion get it from rupture of a bony focus in the spine.

Aseptic meningitis, or sterile meningitis, is a condition in which the layers lining the brain, the meninges, become inflamed and a pyogenic bacterial source is not to blame. Meningitis is diagnosed on a history of characteristic symptoms and certain examination findings (e.g., Kernig's sign). Investigations should show an increase in the number of leukocytes present in the cerebrospinal fluid (CSF) obtained via lumbar puncture (normally being fewer than five visible leukocytes per microscopic high-power field).

The term "aseptic" is frequently a misnomer, implying a lack of infection. On the contrary, many cases of aseptic meningitis represent infection with viruses or mycobacteria that cannot be detected with routine methods. While the advent of polymerase chain reaction has increased the ability of clinicians to detect viruses such as enterovirus, cytomegalovirus, and herpes virus in the CSF, many viruses can still escape detection. Additionally, mycobacteria frequently require special stains and culture methods that make their detection difficult. When CSF findings are consistent with meningitis, and microbiologic testing is unrevealing, clinicians typically assign the diagnosis of aseptic meningitis—making it a relative diagnosis of exclusion.

Aseptic meningitis can result from non-infectious causes as well. it can be a relatively infrequent side effect of medications, or be a result of an autoimmune disease. There is no formal classification system of aseptic meningitis except to state the underlying cause, if known. The absence of bacteria found in the spinal fluid upon spinal tap, either through microscopic examination or by culture, usually differentiates aseptic meningitis from its pyogenic counterpart.

"Aseptic meningitis", like non-gonococcal urethritis, non-Hodgkin lymphoma and atypical pneumonia, merely states what the condition is not, rather than what it is. Terms such as viral meningitis, bacterial meningitis, fungal meningitis, neoplastic meningitis and drug-induced aseptic meningitis can provide more information about the condition, and without using one of these more specific terms, it is difficult to describe treatment options or prognosis.

The following is a list of common signs and symptoms found with neonatal meningitis.

- Fever

- poor appetite

- anterior fontanelle bulging

- seizure

- jitteriness

- dyspnea

- irritability

- anorexia

- vomiting

- diarrhea

- abdominal distention (increase in abdominal size)

- neck rigidity

- cyanosis

- jaundice

- and sunset eyes (downward gaze of the eyes)

- abnormal body temperature (hypo-or hyperthermia)

- change of activity (lethargy or irritability)

Unfortunately these symptoms are unspecific and may point to many different conditions.

Neonatal meningitis is a serious medical condition in infants. Meningitis is an inflammation of the meninges (the protective membranes of the central nervous system (CNS)) and is more common in the neonatal period (infants less than 44 days old) than any other time in life and is an important cause of morbidity and mortality globally. Mortality is roughly half in developing countries and ranges from 8%-12.5% in developed countries.

Symptoms seen with neonatal meningitis are often unspecific that may point to several conditions, such as sepsis (whole body inflammation). These can include fever, irritability, and dyspnea. The only method to determine if meningitis is the cause of these symptoms is lumbar puncture (LP; an examination of the cerebrospinal fluid).

The most common causes of neonatal meningitis is bacterial infection of the blood, known as bacteremia (specifically Group B "Streptococci" (GBS; "Streptococcus agalactiae"), "Escherichia coli", and "Listeria monocytogenes"). Although there is a low mortality rate in developed countries, there is a 50% prevalence rate of neurodevelopmental disabilities in "E. coli" and GBS meningitis, while having a 79% prevalence for non-"E. coli" Gram-negative caused meningitis. Delayed treatment of neonatal meningitis may cause include cerebral palsy, blindness, deafness, and learning deficiencies.

Mollaret's meningitis is characterized by chronic, recurrent episodes of headache, stiff neck, meningismus, and fever; cerebrospinal fluid (CSF) pleocytosis with large "endothelial" cells, neutrophil granulocytes, and lymphocytes; and attacks separated by symptom-free periods of weeks to years; and spontaneous remission of symptoms and signs. Many people have side effects between bouts that vary from chronic daily headaches to after-effects from meningitis such as hearing loss and visual impairment, nerve pain and twitches. Symptoms may be mild or severe. Some cases may be short, lasting only 3–7 days, while others last for weeks to months.

While herpes simplex and varicella can cause rash, Mollaret's patients may or may not have a rash. Herpes simplex virus is likely the most common cause of Mollaret's meningitis.

Viral meningitis, also known as aseptic meningitis, is a type of meningitis due to a viral infection. It results in inflammation of the meninges (the membranes covering the brain and spinal cord). Symptoms commonly include headache, fever, sensitivity to light, and neck stiffness.

Viruses are the most common cause of aseptic meningitis. Most cases of viral meningitis are caused by enteroviruses (common stomach viruses). However, other viruses can also cause viral meningitis. For instance, West Nile virus, mumps, measles, herpes simplex types I and II, varicella, and lymphocytic choriomeningitis (LCM) virus. Based on clinical symptoms, viral meningitis cannot be reliably differentiated from bacterial meningitis, although viral meningitis typically follows a more benign clinical course. Viral meningitis has no evidence of bacteria present in cerebral spinal fluid (CSF). Therefore, lumbar puncture with CSF analysis is often needed to identify the disease.

In most causes there is no specific treatment, with efforts generally aimed at relieving symptoms (headache, fever, or nausea). A few viral causes, such as HSV, have specific treatments.

In the United States viral meningitis is the cause of greater than half of all cases of meningitis. From 1988–1999, about 36,000 cases occurred a year. While the disease can occur in both children and adults it is more common in children.

Mollaret's meningitis is a recurrent or chronic inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. Since Mollaret's meningitis is a recurrent, benign (non-cancerous), aseptic meningitis, it is now referred to as benign recurrent lymphocytic meningitis. It was named for Pierre Mollaret, the French neurologist who first described it in 1944.

Although chronic meningitis has been defined as "irritation and inflammation of the meninges persisting for more than 4 weeks being associated with pleocytosis in the cerebrospinal fluid", cerebrospinal fluid abnormalities may not be detectable for the entire time. Diagnosis can be elusive, as Helbok et al. note: "in reality, many more weeks, even months pass by until the diagnosis is established. In many cases the signs and symptoms of chronic meningitis not only persist for periods longer than 4 weeks, they even progress with continuing deterioration, i. e. headache, neck stiffness and even low grade fever. Impairment of consciousness, epileptic seizures, neurological signs and symptoms may evolve over time."

Fever, headache, and neurological problems, while classic, only occur in 20% of people with brain abscess.

The famous triad of fever, headache and focal neurologic findings are highly suggestive of brain abscess. These symptoms are caused by a combination of increased intracranial pressure due to a space-occupying lesion (headache, vomiting, confusion, coma), infection (fever, fatigue etc.) and focal neurologic brain tissue damage (hemiparesis, aphasia etc.).

The most frequent presenting symptoms are headache, drowsiness, confusion, seizures, hemiparesis or speech difficulties together with fever with a rapidly progressive course. Headache is characteristically worse at night and in the morning, as the intracranial pressure naturally increases when in the supine position. This elevation similarly stimulates the medullary vomiting center and area postrema, leading to morning vomiting.

Other symptoms and findings depend largely on the specific location of the abscess in the brain. An abscess in the cerebellum, for instance, may cause additional complaints as a result of brain stem compression and hydrocephalus. Neurological examination may reveal a stiff neck in occasional cases (erroneously suggesting meningitis).

The patient with meningococcal meningitis typically presents with high fever, nuchal rigidity (stiff neck), Kernig's sign, severe headache, vomiting, purpura, photophobia, and sometimes chills, altered mental status, or seizures. Diarrhea or respiratory symptoms are less common. Petechiae are often also present, but do not always occur, so their absence should not be used against the diagnosis of meningococcal disease. Anyone with symptoms of meningococcal meningitis should receive intravenous antibiotics before the results of lumbar puncture, as delay in treatment worsens the prognosis.

Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present irritability, poor appetite and fever.

Neurological examinations usually reveal a drowsy or confused patient. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningoencephalitis.

Symptoms of meningococcemia are, at least initially, similar to those of influenza. Typically, the first symptoms include fever, nausea, myalgia, headache, arthralgia, chills, diarrhea, stiff neck, and malaise. Later symptoms include septic shock, purpura, hypotension, cyanosis, petechiae, seizures, anxiety, and multiple organ dysfunction syndrome. Acute respiratory distress syndrome and altered mental status may also occur. The petichial rash appear with the 'star-like' shape. Meningococcal sepsis has a greater mortality rate than meningococcal meningitis, but the risk of neurologic sequelae is much lower.

Neurosyphilis has four different forms: asymptomatic, meningovascular, tabes dorsalis, and general paresis. In rare instances, active neurosyphilis can mimic Alzheimer's disease.

Symptoms of neurosyphilis include, but are not limited to the following:

- Abnormal gait

- Blindness

- Confusion, disorientation

- Sudden personality changes

- Changes in mental stability

- Dementia

- Depression

- Headache

- Fecal and urinary incontinence

- Irritability

- Memory problems

- Mood disturbances

- Numbness in the toes, feet, or legs

- Poor concentration

- Psychosis

- Seizures

- Neck stiffness

- Tremors

- Visual disturbances. There may be the sign of Argyll Robertson pupils, which are bilateral small pupils that constrict when the patient focuses on a near object but do not constrict when exposed to bright light.

- Muscle weakness

Upon further diagnostic workup, the following signs may be present:

- Abnormal reflexes

- Muscle atrophy

- Muscle contractions

Anaerobic and microaerophilic cocci and gram-negative and gram-positive anaerobic bacilli are the predominate bacterial isolates. Many brain abscesses are polymicrobical. The predominant organisms include: "Staphylococcus aureus", aerobic and anaerobic streptococci (especially "Streptococcus intermedius"), "Bacteroides", "Prevotella", and "Fusobacterium" species, Enterobacteriaceae, "Pseudomonas" species, and other anaerobes. Less common organisms include: "Haemophillus influenzae", "Streptococcus pneumoniae" and "Neisseria meningitides".

Bacterial abscesses rarely (if ever) arise "de novo" within the brain, although establishing a cause can be difficult in many cases. There is almost always a primary lesion elsewhere in the body that must be sought assiduously, because failure to treat the primary lesion will result in relapse. In cases of trauma, for example in compound skull fractures where fragments of bone are pushed into the substance of the brain, the cause of the abscess is obvious. Similarly, bullets and other foreign bodies may become sources of infection if left in place. The location of the primary lesion may be suggested by the location of the abscess: infections of the middle ear result in lesions in the middle and posterior cranial fossae; congenital heart disease with right-to-left shunts often result in abscesses in the distribution of the middle cerebral artery; and infection of the frontal and ethmoid sinuses usually results in collection in the subdural sinuses.

Herpesviral meningitis is meningitis associated with herpes simplex virus (HSV).

HSV-2 is the most common cause of Mollaret's meningitis, a type of recurrent viral meningitis. This condition was first described in 1944 by French neurologist Pierre Mollaret. Recurrences usually last a few days or a few weeks, and resolve without treatment. They may recur weekly or monthly for approximately 5 years following primary infection.

Encephalitis is inflammation of the brain. Severity is variable. Symptoms may include headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations, trouble speaking, memory problems, and problems with hearing.

Causes of encephalitis include viruses such as herpes simplex virus or rabies, bacteria, fungus, or parasites. Other causes include autoimmune diseases and certain medication. In many cases the cause remains unknown. Risk factors include a weak immune system. Diagnosis is typically based on symptoms and supported by blood tests, medical imaging, and analysis of cerebrospinal fluid.

Certain types are preventable with vaccines. Treatment may include, antiviral medication (such as acyclovir), anticonvulsants, and corticosteroids. Treatment generally takes place in hospital. Some people require artificial respiration. Once the immediate problem is under control, rehabilitation may be required. In 2015, encephalitis was estimated to have affected 4.3 million people and resulted in 150,000 deaths worldwide.

Although DNA analysis techniques such as Polymerase chain reaction can be used to look for DNA of herpesviruses in spinal fluid or blood, the results may be negative, even in cases where other definitive symptoms exist.

Characteristics of a viral infection can include pain, swelling, redness, impaired function, fever, drowsiness, confusion and convulsions.

LCMV infection manifests itself in a wide range of clinical symptoms, and may even be asymptomatic for immunocompetent individuals. Onset typically occurs between one or two weeks after exposure to the virus and is followed by a biphasic febrile illness. During the initial or prodromal phase, which may last up to a week, common symptoms include fever, lack of appetite, headache, muscle aches, malaise, nausea, and/or vomiting. Less frequent symptoms include a sore throat and cough, as well as joint, chest, and parotid pain. The onset of the second phase occurs several days after recovery, and consists of symptoms of meningitis or encephalitis. Pathological findings during the first stage consist of leukopenia and thrombocytopenia. During the second phase, typical findings include elevated protein levels, increased leukocyte count, or a decrease in glucose levels of the cerebrospinal fluid).

Occasionally, a patient improves for a few days, then relapses with aseptic meningitis, or very rarely, meningoencephalitis.

Patients with meningitis may have a stiff neck, fever, headache, myalgia, nausea and malaise. In some occasions, meningitis occurs without a prodromal syndrome. Meningoencephalitis is characterized by more profound neurological signs such as confusion, drowsiness, sensory abnormalities and motor signs. Under reported complications include myelitis, Guillain–Barré-type syndrome, cranial nerve palsies, transient or permanent hydrocephalus, sensorineural hearing loss, orchitis, arthritis and parotitis. LCMV infections have also been associated with pancreatitis, pneumonitis, myocarditis and pericarditis. The entire illness usually lasts 1 to 3 weeks, nonetheless, temporary or permanent neurological damage is possible in all central nervous system infections, especially in cases of meningoencephalitis. Chronic infections have not been reported in humans and deaths rarely occur.

CSF rhinorrhoea refers to the drainage of cerebrospinal fluid through the nose. Measures of CSF components such as glucose have been used in the past, but are neither sensitive nor specific; beta-2 transferrin, however, has been shown to have a high positive predictive value. It has also been noted to be characterized by unilateral discharge.

It is a sign of basal skull fracture. Management includes watchful waiting - leaks often stop spontaneously; if this does not occur then neurosurgical closure is necessary to prevent the spread of infection to the meninges.

Other signs of basal skull fracture includes CSF otorrhoea (drainage of CSF through the ear). It can have devastating complications in some patients, as the communication between the nasal cavity and the cerebrospinal fluid and CNS can result in bacterial infections of the CNS that can have catastrophic effects on the patient.

CSF rhinorrhoea can also be a symptom of a pituitary adenoma.

Spontaneous CSF rhinorrhea. The most common congenital or acquired defect in the skull base bones (anterior cranial fossa) at the spontaneous nasal liquorrhea localized in following formation:

- sphenoid sinus (43%)

- ethmoid bone (29%)

- cribriform plate (29%)

In addition to evaluation of any symptoms and signs, various blood tests can be done:

- Venereal Disease Research Laboratory test (VDRL)

- Fluorescent treponemal antibody absorption (FTA-ABS)

- Rapid plasma reagin (RPR)

- Treponema pallidum particle agglutination assay (TPPA)

Also, it is important to test the cerebrospinal fluid for signs of syphilis.

Additional tests to look for problems with the nervous system may include the following:

- Cerebral angiogram

- Head CT scan

- Lumbar puncture ("spinal tap") to acquire a sample for cerebrospinal fluid analysis

- MRI scan of the brain, brainstem, or spinal cord

Lymphocytic choriomeningitis is a particular concern in obstetrics, as vertical transmission is known to occur. For immunocompetent mothers, there is no significant threat, but the virus has damaging effects upon the fetus. If infection occurs during the first trimester, LCMV results in an increased risk of spontaneous abortion. Later congenital infection may lead to malformations such as intracranial calcifications, hydrocephalus, microcephaly or macrocephaly, intellectual disabilities, and seizures. Other findings include chorioretinal scars, and optic atrophy. Chorioretinitis, which is followed by chorioretinal scarring, is the most common ocular lesion. Mortality among infants is approximately 30%. Among the survivors, two thirds have lasting neurologic abnormalities.

Other ocular defects including optic atrophy, microphthalmia, vitreitis, leukokoria and cataracts can also be seen. Most of the infants in one case series were of normal birth weight, although 30% were underweight. Aspiration pneumonia can be a fatal complication. Infants who survive may have severe neurological defects including epilepsy, impaired coordination, visual loss or blindness, spastic diplegia or quadriparesis/quadriplegia, delayed development and intellectual disability. Less severe cases with isolated cerebellar hypoplasia and symptoms of ataxia and jitteriness have been reported occasionally. There have also been rare cases with evidence of chorioretinitis but without neurological signs. Systemic signs seem to be rare, but hepatosplenomegaly, thrombocytopenia and hyperbilirubinemia have been documented in a few cases, and skin blisters were reported in one infant.

If a woman has come into contact with a rodent during pregnancy and LCM symptoms are manifested, a blood test is available to determine previous or current infection. A history of infection does not pose a risk for future pregnancies.