Brachial plexopathy from Lyme disease can present as progressive arm weakness, neck pain, and shock-like pains radiating from shoulders — initially misdiagnosed as cellulitis or peripheral nerve injury. A 76-year-old man developed left arm weakness following what he thought was a mosquito bite, received antibiotics for presumed cellulitis with temporary improvement, then returned 24 days later with bilateral paroxysmal “shock-like” pains and worsening weakness. MRI revealed polyradiculitis along the brachial plexus and spinal cord, and Lyme testing confirmed meningoradiculitis requiring IV ceftriaxone for complete recovery over one year.

Initial Presentation: Arm Weakness and Neck Pain

In their article “Early Lyme neuroborreliosis manifesting as brachial plexopathy and meningitis in Northwestern Ontario, Canada,” Gu and colleagues describe a case of Lyme disease presenting as brachial plexopathy and meningitis.

The 76-year-old man was initially admitted to the hospital with left arm weakness and neck pain. He also had a 3-day history of body aches and headaches.

He reported having what he believed to be a mosquito bite, which became increasingly red and swollen. But he did not notice any ticks attached to his skin.

The combination of arm weakness, neck pain, body aches, and headaches after a suspected insect bite should have raised suspicion for tick-borne infection. But without recognizing the bite as a tick, the diagnosis was missed.

What Is Brachial Plexopathy?

Brachial plexopathy is a form of peripheral neuropathy which occurs when there is damage to the brachial plexus. This is a group of nerves that run from the lower neck through the upper shoulder area.

The brachial plexus consists of nerve roots C5-T1 that merge and divide to form the nerves supplying the arm, shoulder, and hand. Damage to these nerves causes:

• Weakness in shoulder, arm, or hand muscles
• Pain radiating from neck/shoulder down the arm
• Numbness or tingling in affected areas
• Loss of reflexes
• Muscle atrophy if chronic

Causes include trauma, radiation, tumors, autoimmune disease, and infection — including Lyme disease.

Misdiagnosed as Cellulitis

A diagnosis of purulent cellulitis was made, and he was prescribed a 7-day course of cephalexin. His symptoms resolved.

The red, swollen “bite” was interpreted as cellulitis (skin infection), and cephalexin was prescribed. The temporary improvement likely reflected either: (1) cephalexin has some activity against Borrelia, delaying but not curing infection, or (2) natural fluctuation in symptoms as infection disseminated.

Return 24 Days Later: Shock-Like Pains

However, 24 days later he returned to the emergency department complaining of a mild headache, which he had for several days, along with “bilateral, paroxysmal ‘shock-like’ pains radiating from his shoulders to his arms and chest.”

He was discharged, pending test results.

The “shock-like” pains are pathognomonic for radiculitis — nerve root inflammation causing sudden, electric, stabbing pains along the dermatome. This is a hallmark of neuroborreliosis, particularly Bannwarth syndrome in European literature. The bilateral distribution and radiation pattern from shoulders to arms and chest indicates multiple nerve roots affected (C5-T3 levels).

Progressive Arm Weakness

Over the next few days, the man developed additional weakness in his left arm and hand. Again, he was discharged and awaited further test results.

Five days later, the man returned to the hospital with worsening symptoms. He complained of increased left arm weakness, neck pain and occasional night sweats.

The progressive weakness despite initial antibiotic treatment indicated inadequate therapy. Cephalexin doesn’t penetrate the central nervous system well enough to treat neuroborreliosis. The night sweats are a systemic symptom of disseminated infection.

MRI Reveals Polyradiculitis

Test results showed “increased signal uptake along the ventral aspect of the spinal cord at T3 and along the left brachial plexus, which was felt to be in keeping with polyradiculitis,” the authors wrote.

Lyme disease testing was positive by both ELISA and Western blot.

The MRI findings were diagnostic: inflammation along multiple nerve roots (polyradiculitis) affecting the brachial plexus and thoracic spinal cord. This isn’t peripheral nerve damage from trauma or compression — it’s inflammatory radiculoneuritis from infection.

Diagnosis and Treatment

“The patient was diagnosed with meningoradiculitis as a manifestation of early [Lyme neuroborreliosis]” and began treatment with IV ceftriaxone.

“Over the subsequent year, he had eventual complete recovery in muscle strength and sensation, with slower improvement to the cervical neck and left arm pain,” the authors wrote.

Meningoradiculitis means inflammation of both the meninges (meningitis) and nerve roots (radiculitis). This is the full spectrum of early disseminated neuroborreliosis. The one-year recovery timeline is typical for severe neurologic Lyme — nerve damage takes months to heal even after spirochetes are killed.

Why Lyme Disease Causes Brachial Plexopathy

Brachial plexopathy from Lyme disease occurs when spirochetes invade nerve roots in the cervical and upper thoracic spine (C5-T1), causing inflammatory radiculoneuritis. The mechanisms include:

• Direct spirochetal invasion: Borrelia organisms infiltrate nerve root sheaths and surrounding tissues
• Inflammatory response: Immune cells (lymphocytes, macrophages) attack infected nerve roots
• Meningeal spread: Spirochetes in CSF access nerve roots as they exit the spinal cord
• Edema and compression: Inflammation causes swelling, compressing nerve fibers
• Demyelination: Inflammatory damage to myelin sheaths impairs nerve conduction

The result: pain, weakness, sensory loss, and reflex changes in the affected arm(s).

The Diagnostic Challenge

This case involved multiple misdiagnoses and delays:

Day 1: Arm weakness, neck pain, headache → Diagnosed as cellulitis, given cephalexin
Day 24: Returns with shock-like pains → Discharged pending tests
Day 29: Progressive arm weakness → Discharged pending tests
Day 34: Worsening symptoms, night sweats → MRI finally ordered
Day 34+: Lyme diagnosed, IV ceftriaxone started

This represents over one month from symptom onset to appropriate treatment — time during which neurologic damage progressed.

Clinical Perspective

This case demonstrates how brachial plexopathy from Lyme disease gets misdiagnosed when physicians don’t recognize the pattern. The initial presentation — arm weakness and neck pain after an insect bite — could suggest peripheral nerve injury, cervical radiculopathy from disc herniation, or stroke. Without considering tick-borne infection, the correct diagnosis is missed.

The misdiagnosis as cellulitis is understandable — a red, swollen bite site looks like skin infection. But when arm weakness and neck pain accompany the “cellulitis,” this suggests deeper involvement: lymphangitis, septic arthritis, or as in this case, early disseminated infection affecting the nervous system.

The temporary improvement after cephalexin likely contributed to diagnostic confusion. When symptoms improve with antibiotics, the presumptive diagnosis seems confirmed. But cephalexin has modest activity against Borrelia and doesn’t achieve adequate CSF levels. Temporary improvement represents partial treatment, not cure.

The shock-like pains 24 days later are the key diagnostic clue. These paroxysmal, electric, shooting pains radiating from shoulders to arms and chest are classic for radiculoneuritis. They don’t occur with cellulitis, peripheral nerve injury, or degenerative spine disease. This symptom pattern should immediately prompt consideration of inflammatory radiculopathy — and in endemic areas, Lyme disease.

The bilateral distribution is significant. Unilateral brachial plexopathy might suggest trauma, tumor compression, or thoracic outlet syndrome. Bilateral involvement indicates systemic disease — infection, autoimmune disorder, or malignancy.

The progressive weakness despite initial antibiotics proved the diagnosis was wrong. When neurologic symptoms worsen after starting treatment, this signals either incorrect diagnosis, inadequate treatment, or resistant infection. In this case, it was inadequate treatment — cephalexin doesn’t treat neuroborreliosis.

The MRI findings validated the clinical suspicion. Enhancement along nerve roots and spinal cord confirms inflammation, not mechanical compression or ischemia. This pattern is diagnostic for radiculoneuritis.

The complete recovery over one year demonstrates the reversibility of Lyme-induced nerve damage when treated appropriately. Unlike degenerative or traumatic nerve injury, infection-induced radiculoneuritis can heal completely. But recovery is slow — months to years — requiring patient reassurance and continued monitoring.

Finally, the authors’ conclusion about missed EM rash and tick bites is critical. This patient never saw a tick attached. He thought the bite was from a mosquito. Without recognizing tick exposure, Lyme disease drops off the differential. This is why clinical pattern recognition is essential — when symptoms fit neuroborreliosis (radicular pain, arm weakness, meningitis), Lyme should be tested regardless of tick bite history.

Authors’ Conclusions

“A history of EM rash or black-legged tick bite may go unrecognized. Therefore, patients with new cranial (especially facial) neuropathy, painful radiculitis, or aseptic meningitis, who present in a Lyme endemic area during or shortly after tick season should be alert to the possibility of early [Lyme neuroborreliosis.]”

Frequently Asked Questions

Can Lyme disease cause brachial plexopathy?

Yes. Brachial plexopathy from Lyme disease occurs when spirochetes invade nerve roots in the cervical spine (C5-T1), causing inflammatory radiculoneuritis with arm weakness, pain, and shock-like sensations radiating down the arms.

What are shock-like pains in Lyme disease?

Shock-like or electric pains are paroxysmal stabbing sensations caused by nerve root inflammation (radiculitis). They radiate along specific dermatomes and are a hallmark of neuroborreliosis, particularly early disseminated Lyme disease.

Can cellulitis antibiotics treat Lyme disease?

Partially. Cephalexin has modest activity against Borrelia but doesn’t penetrate the CNS adequately. It may cause temporary improvement but won’t cure neuroborreliosis, leading to relapse and progression as in this case.

How long does recovery from Lyme brachial plexopathy take?

This patient had complete recovery over one year. Nerve healing is slow even after spirochetes are killed with antibiotics. Recovery timeline depends on severity of nerve damage and how quickly treatment was initiated.

Why was Lyme disease not considered initially?

The patient thought the bite was from a mosquito, not a tick. Without recognized tick exposure, Lyme disease wasn’t on the differential. This is why pattern recognition (radicular pain, progressive weakness, meningitis) is essential even without tick bite history.

What is meningoradiculitis?

Meningoradiculitis is combined inflammation of the meninges (meningitis) and nerve roots (radiculitis). It represents early disseminated neuroborreliosis affecting both central nervous system membranes and peripheral nerve roots exiting the spinal cord.

Can brachial plexopathy be bilateral in Lyme disease?

Yes. This patient had bilateral shock-like pains affecting both arms, though left-sided weakness was more pronounced. Bilateral involvement indicates systemic disease (infection, autoimmune) rather than localized trauma or compression.