Neurological Disorders: Porphyric Neuropathy

Introduction

Porphyric Neuropathy results due to damage to the peripheral nerves by porphrin metabolites.

Porphyrins are chemical molecules and they take part in the synthesis of the heme component of hemoglobin, the pigmented molecule present inside the RBCs (red blood cells) as well other pigments like myoglobin, enzymes like catalase etc. If there is any defect in the proper synthesis of heme then the precursor molecules accumulate in the body and they can act as toxic irritant to various organs & tissues of the body.

There are many different types of porphyrias and generally they are grouped under cutaneous (skin related) or hepatic (liver related) types. From the neurological point of view AIP (acute intermittent porphyria) is the most important and it is a type of hepatic porphyria and results from a deficiency of PBG (porphobilinogen) deaminase enzyme.

In the case of AIP, porphyrin precursors that get accumulated in the body can act as a toxic irritant to peripheral nerves, gastrointestinal tract, brain etc.

Who gets it?

It is an AD (autosomal dominant) type of inherited disease. The disease may be precipitated by certain medications, toxins, hormones, infetions etc.Women are generally more prone to this disease than men. The disease manifests in young and middle aged adults more than other age groups.

Although it is a genetic disease it does not generally manifest unless one or more of the trigger factors mentioned above are present.

How does a patient with this neuropathy present?

• Neuropathic symptoms like numbness, pain, tingling, muscle weakness etc
• Abdominal pain
• Constipation
• Nausea, Vomiting
• Fever
• Heart rate changes
• Seizures
• Psychiatric manifestations etc

Some of the above manifestations are due to irritation of the autonomic nervous system by the porphyrins.

Diagnosis

High index of clinical suspicion is necessary. Urine should be sent for porphyrin molecules detection. Urine also produces a characteristic color on standing. Estimation of PBG deaminase enzyme concentration and DNA tests for genetic mutation are other options.

An EMG/NCS (electromyography & nerve conduction study) may help in picking up the neuropathy condition.

Treatment/Management

The following therapeutic interventions are done on case to case basis;

• Intravenous glucose
• Hematin
• Neuropathy treatment (medications like gabapentin for pain, numbness)
• Seizures are treated with benzodiazepines (e.g. diazepam), gabapentin etc
• If cardiac arrhythmias are present (irregular heart beats) they are treated appropriately

Patients are advised to avoid using certain medications (there is a big list of it), hormonal preparations, toxins etc to prevent future attacks.

A Neurologist is frequently involved in the care of patients with Porphyric Neuropathy.



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