Neuropathic Pain with Neuralgic Features
70-year-old female with a history of diabetes mellitus began experiencing pain in the legs. In the last few months the pain localized in her inner thighs. It is burning in nature, with sudden intense attacks, and is consistent with neuropathic pain with neuralgic features. The expert suggests possible diagnosis, further investigation and symptomatic treatment. In his opinion, it is likely that the cause of the symptoms is peripheral neuropathy or radiculopathy.
The patient asks about the cause of her symptoms, and about the treatment options.
This is a 70 year old woman with a history of diabetes mellitus, arterial hypertension, abdominal aortic aneurysm and hypercholesterolemia. In 2004, she began experiencing pain in the legs. The pain was initially non-localizing and was burning in nature. In the last few months the pain localized more in the inner thighs. The pain seems to appear in sudden attacks, it is intense, making it impossible for her to walk and causing frequent falls.
Blood test, electromyogram (EMG) and echo color Doppler of the legs are reported to be normal. A thorough vascular investigation demonstrated moderate widespread vascular disease.
The nature of the symptoms: initially burning pain with sudden intense (shock-like) attacks, is consistent with neuropathic pain with neuralgic features.
Her symptoms are not typical for intermittent claudication. I do not think that her peripheral vascular disease or venous insufficiency in the legs are responsible for her symptoms.
I would suggest to focus on a neurological source for the patient's symptoms. Since I have not been provided with the findings of the neurological examination, I cannot make a definite statement regarding the cause of her symptoms, but rather suggest possible diagnosis, further investigation and symptomatic treatment.
It seems to me that this neuropathic pain is most likely the result of peripheral nervous system (PNS) abnormalities, unless the neurological examination indicates for a higher lesion. Since no muscle wasting or permanent muscle weakness is mentioned, I assume that the symptoms are primarily sensory. Such type of neuropathic pain accompanied with neuralgic attacks (the sudden intense pain) suggests that it is likely that the cause of symptoms is peripheral neuropathy or radiculopathy. The lack of motor symptoms and the symmetry of her sensory complaints are against lumbosacral plexopathy as the source of the symptoms.
Sensory peripheral neuropathy usually begins distally in the feet (“socks” distribution), the pain is usually burning in nature, and it is often accompanied with tingling, numbness and allodynia. The patient's symptoms are not typical for neuropathy, since initially the pain was not localized distally, and recently the attacks have been localized to the inner thighs. Moreover, the EMG was reported to be normal.
However, sensory neuropathy that predominantly affects the small nerve fibers (small fiber neuropathy) is often not demonstrated in the EMG studies and the symptoms can be patchy or diffuse. This type of neuropathy can be associated with diabetes and can be a possible explanation for the clinical picture. I would therefore suggest to perform quantitative sensory testing (QST) in order to assess the small nerve fibers. QST is a complementary test in the investigation of neuropathies when EMG fails to demonstrate abnormalities of the small nerve fibers. I would also suggest to perform a neuropathy work up, including: CBC, biochemistry, B12, TSH, RF, ANA, ENA, immunofixation electophoresis, serologic tests for hepatitis C and B.
Root lesion (radiculopathy) can be a possible explanation for the patient's symptoms. The lancinating pain to the inner aspects of the thighs can be caused by L2-3 root lesion. Rarely, vascular malformation, such as tortuous veins, surrounding the roots or spinal cord can cause neurological symptoms. In such cases, there is no back pain and the symptoms are purely neurological. Of course, any other process in the spinal canal can produce similar symptoms. Therefore, I would suggest MRI/MRA of the lumbar and thoracic spine. Of note, neuropathy and radiculopathy may co-exist. The presence of diabetes even with mild neuropathy may render the roots more susceptible to any sort of insult.
Since the pain is clearly neuropathic and has neuralgic features, I advise that empirical treatment against neuropathic pain be considered. I suggest treatment with Pregabaline (Lyrica) 300 mg/day devided in two doses. In order to avoid side effects it is advisable to start with 75 mg before bedtime and increase the dosage by 75 mg every third day. In the future, if needed, other anti-neuropathic pain medications, such as: Duloxetine, Carbamazepine, Amitriptyline etc, can be tried.