Exertional Painless Weakness: Chronic Inflammatory Demyelinating Polyradiculoneuropathy in a Recreational Runner

Introduction

Exertional painless weakness in the running athlete can have similar differential diagnoses to exertional leg pain, a more common complaint (¹). Possible etiologies linked to exertional leg pain include musculoskeletal, vascular, or neuromuscular conditions. These conditions include stress injuries, chronic exertional compartment syndrome (CECS), external iliac artery endofibrosis, popliteal artery entrapment syndrome, and lower extremity nerve entrapment (¹). In the rare presentation of exertional weakness without pain, neurologic and neuromuscular conditions should be higher in the differential diagnosis. These conditions can vary in clinical presentation, severity, prognosis, and treatment. A possible, but uncommon diagnosis is chronic inflammatory demyelinating polyneuropathy (CIDP), which is not usually part of an exertional leg pain clinical scenario (^1,2).

The prevalence of CIDP ranges from one to nine cases per 100,000 persons, making it the most common treatable chronic neuropathy worldwide (^2–4). The typical clinical presentation involves a relapsing or progressive neuropathy with proximal and distal weakness that develops over more than an 8-wk period (^5,6). The exact mechanism underlying CIDP is still not well defined, but it is classified as an autoimmune disorder in which an abnormal immune response is targeted toward components of peripheral nerves, resulting in demyelination and axonal damage (⁵). Patients can be successfully treated with intravenous immunoglobulin (IVIG), corticosteroids, and plasma exchange, but some may experience lasting disability regardless of treatment (^6,7).

Currently, there is limited evidence regarding neuromuscular diseases in athletes, especially CIDP in recreational runners. High suspicion is needed to diagnose these conditions in runners with an initial presentation of subtle leg weakness. Because of the high degree of diagnostic and therapeutic value that comes from early identification of this rare diagnosis in a sports medicine clinic, this case report aims to increase awareness of the disease for the sports medicine provider.

Case Description

A 50-year-old male long-distance runner presented to a sports medicine clinic with 4 months of bilateral lower extremity fatigue while running. His exercise routine consisted of running 3 miles daily until he started noticing bilateral leg heaviness, as if his legs were shutting down. This progressed slowly to the point where he could barely complete a three-quarter mile jog without having to stop. These symptoms worsened with increased mileage and improved with rest. He denied symptoms when walking, associated pain, numbness, tingling, burning, swelling, skin discoloration, toxic habits, or relevant family medical history. At first, he went to physical therapy, since he thought this was related to his past history of medial tibial stress syndrome. After a few weeks of progression of symptoms and limitation on his exercise routine, the physical therapist referred him to a sports medicine clinic for evaluation (Table 1).

Table 1 - Timetable Highlighting Clinical Presentation and Diagnostic Process

Day	Description of events/findings
0	Patient experienced lower-extremity fatigue while running, eventually becoming unable to complete his full running routine.
120	Initial PM&R sports medicine clinic visit: MMT was intact except for a 4/5 strength on bilateral extensor hallucis muscles and bilateral dorsiflexion. DTRs were diminished throughout (+1). Laboratory and ABI tests and electrodiagnostic studies ordered.
132	Laboratory and ABI tests: normal findings. Electrodiagnostic test: revealed a demyelinating motor and sensory neuropathy with temporal dispersion and conduction block. Neuromuscular service was consulted.
160	Neuromuscular service visit: worsening of weakness in the same myotomes with new evidence of weakness in wrist extension. Lumbar puncture with CSF analysis was ordered to confirm the suspicion.
163	CSF analysis: High protein and high protein/albumin ratio, consistent with CIDP diagnosis.
175-177	Started IVIG, administered 3 d in a row.
182	Clinical improvement and began running short distances; changed IVIG treatment to every 2 wk
252	Neurology follow-up visit: patient reported improvement of symptoms.
254	PM&R follow-up visit: patient reported improvement of symptoms and stated he began running 3 miles with no symptoms.
273	Patient continued with IVIG every 2 wk. Patient clinically improved and continued treatment and follow-up appointments accordingly.

ABI, ankle-brachial index; DTRs, deep tendon reflexes; MMT, manual muscle testing; PM&R, Department of Physical Medicine and Rehabilitation.

During the initial visit, physical examination of the patient's legs did not show any signs of swelling, muscle atrophy, twitching, fasciculation, discoloration, or rashes. There was no tenderness upon palpation, and he had a full range of motion throughout all extremities. Manual muscle testing was intact, except for a 4/5 strength on bilateral extensor hallucis muscles and bilateral dorsiflexion (Table 2). Sensation was grossly intact to both pinprick and soft touch. Deep tendon reflexes were diminished throughout (+1), and all of his extremity pulses were strong. The patient had a normal gait and adequate proprioception and vibration senses. Provocative testing, including hop, straight leg, and facet loading tests, was negative.

Table 2 - Manual Muscle Testing and Physical Examination Findings^a

Myotomes	Initial PM&R evaluation		Initial neuromuscular evaluation		First PM&R Follow-up
	R	L	R	L	R	L
Elbow flexors C5	5	5	5	5	5	5
Wrist extensors C6	5	5	4	4	5	5
Elbow extensors C7	5	5	5	5	5	5
Finger flexors C8	5	5	5	5	5	5
Finger abductors T1	5	5	5	5	5	5
Hip flexors L2	5	5	5	5	5	5
Knee extensors L3	5	5	5	5	5	5
Ankle dorsiflexors L4	4+	4+	4−	4−	5	5
Long toe extensors L5	4+	4+	4−	4−	5	5
Ankle plantar flexors S1	5	5	5	5	5	5
Total	48	48	46	46	50	50

L, left; R, right.

^a Bold emphasis stands for strength deficiencies.

The differential diagnosis included CECS, peripheral artery disease, external iliac artery endofibrosis, popliteal artery entrapment syndrome, lumbar radiculopathy, nerve entrapment, neuromuscular conditions, and overtraining syndrome. The following diagnostic studies were ordered: electrodiagnostic study, basic laboratory studies (i.e., creatine phosphokinase, complete blood cell count, thyroid panel, comprehensive metabolic panel, aldolase, sedimentation rate, C-reactive protein), and an ankle-brachial index test. All tests came back normal except the electrodiagnostic study, which revealed evidence of a demyelinating motor and sensory neuropathy with temporal dispersion and conduction block (Table 3). The electrodiagnostic results revealed a suspicion for a demyelinating polyneuropathy, such as Guillain-Barré syndrome (GBS) or CIDP. Because of the chronicity, CIDP was more likely. Neuromuscular service was consulted, and findings were consistent with worsening of weakness in the same myotomes with new evidence of weakness in wrist extension (Table 2). At that point, the patient started noticing that his foot was slapping on the floor while walking. Lumbar puncture with cerebrospinal fluid (CSF) analysis revealed high protein in CSF consistent with CIDP.

Table 3 - Nerve Conduction Study Results

Nerve	Type	Site	Stim side	Amp	Amp normal	CV	CV normal	Distal lat	Lat normal	F Wave lat	F Wave est
Fibular	Motor	EDB	R	3.2	>2.0	28	>41	5.3	<6.6	—	91.0
Fibular	Motor	Tib ant	R	5.5	>5.1	43	>43	4.5	<6.8	—	—
Tibial	Motor	AH	R	1.0	>4.0	38	>40	6.2	<6.1	92.9	69.9
Sural	Sensory	Ankle	R	7.0	>6.0	59	>40	3.7	<4.5	—	—
Median	Motor	APB	R	3.6	>4.0	29	>48	6.0	<4.5	49.7	50.8
Ulnar	Motor	ADM	R	5.6	>6.0	30	>51	4.5	<3.6	—	47.8
Median	Sensory	DigII	R	10.0	>15.0	38	>56	5.2	<3.6	—	—
Radial	Sensory	Wrist	R	10.0	>20.0	—	>49	3.2	<2.9	—	—
Ulnar	Sensory	Dig V	R	10.0	>10.0	40	>54	3.7	<3.1	—	—

—, not available; ADM, abductor digiti minimi; AH, abductor hallucis; Amp, amplitude; Tib ant, tibialis anterior; APB, abductor pollicis brevis; CV, conduction velocity; EDB, extensor digitorum brevis; Lat, latency; Stim, stimulation.

The patient received three consecutive days of 30 g IVIG infusion therapy followed by treatment every 2 wk for 3 months. He showed marked improvement of symptoms on his follow-up visits. While still on treatment, the patient began to run 1 mile daily without lower extremity weakness or fatigue. During his last visit to the sports medicine clinic, the patient reported resolution of symptoms and stated he was running 3 mile·d⁻¹, 6 d·wk⁻¹.

Discussion

To our knowledge, this is the first documented case of CIDP in a recreational runner with complaint of exertional progressive, painless weakness in the lower extremities. The case portrays the clinical complexity that can arise from a nonspecific chief complaint, such as heavy legs when running. Research has reported that up to 47% of patients with CIDP have been misdiagnosed and started on inappropriate therapy (⁸). This case also displays the importance of including neuromuscular or neuropathic conditions in the differential diagnosis of an athlete presenting with exertional painless weakness.

The presence or absence of pain in addition to other symptoms is key to narrowing the differential diagnosis. Etiologies should be divided into musculoskeletal, vascular, and neurologic and neuromuscular conditions. Common musculoskeletal conditions include stress injuries and CECS (¹). The most common complaint with these conditions is exertional leg pain, but some patients, particularly those with CECS, may present with neurologic symptoms, like foot drop or leg numbness after exertion. The diagnostic study for CECS is compartment pressure testing, which usually causes discomfort to the patient (¹).

Regarding vascular conditions, peripheral artery disease, external iliac artery endofibrosis, and popliteal artery entrapment syndrome should be considered when evaluating an athlete with exertional leg pain or weakness (¹). Usually, these conditions may present with paresthesia, claudication, leg swelling, weakness, or fatigue. Ankle-brachial index is a good study to begin evaluating vascular issues, but other diagnostic tests can be performed, such as magnetic resonance angiography and computed tomography angiography (¹).

Neuromuscular conditions affect the muscles and nerves, thus limiting functionality, mobility, independence, and performance. Some of these conditions may be painful, while others are not (^1–3). Lower-extremity nerve entrapment is usually a painful neuromuscular condition, but sometimes, it can present with only paresthesia and weakness (¹). Electrodiagnostic evaluation can help confirm the diagnosis, localize the lesion or entrapment, and determine the severity and prognosis (⁷). However, if extremity weakness without pain is the issue, other neurologic conditions should be considered, including spinal cord compression, CIDP, GBS, amyotrophic lateral sclerosis, multiple sclerosis, inflammatory myopathies, myasthenia gravis, and Lambert-Eaton syndrome. A detailed family history can help determine the likelihood of these diagnoses.

There is general agreement on the criteria for diagnosis of the classic form of CIDP (⁹). Time frame and progression of symptoms are very important to distinguish GBS from CIDP, considering their overlapping features. Upon history, progression should be at least 2 months to consider CIDP as a possible diagnosis, while GBS usually presents within 1 wk to 6 wk of antecedent illness (^7,9). Additionally, classic GBS usually is a monophasic condition presenting with ascending weakness, while CIDP is considered a relapsing or progressive disease (^7,9). On physical examination, careful monitoring of clinical features of demyelination is essential, with weakness usually outweighing sensory issues in CIDP. Extremity weakness commonly exhibits the same degree of proximal and distal involvement (^6,7,9,10). Our patient initially presented with distal lower-extremity weakness and progressed to weakness in distal upper extremity. Globally diminished reflexes are another reported physical finding that serves as a generally accepted criterion for CIDP. During the first evaluation, our patient had decreased lower extremity reflexes, which triggered suspicion for a neurologic disease. Any time that a patient presents with symmetric hyporeflexia, a neurological condition should be considered.

In addition to clinical presentation, a series of diagnostic studies, including electrodiagnostic studies, lumbar puncture, and nerve biopsy, can be used to confirm CIDP. Typical electrodiagnostic findings of CIDP are reduced latency, conduction block, temporal dispersion, and reduced conduction velocity in the motor and sensory nerves (⁶). Delayed diagnosis can increase the likelihood of disease progression causing axonal loss. For this reason, early electrophysiologic studies aid in determining if there is superimposed axonal damage, which is usually seen in patients with poor prognoses (⁷).

As mentioned above, another important diagnostic study in CIDP is lumbar puncture for CSF analysis. In CIDP, CSF analysis shows high protein and high protein-to-albumin ratio. Rarely needed, nerve biopsy may be a helpful tool when a clear diagnosis cannot be determined with the abovementioned criteria. Nerve biopsy was not needed to confirm CIDP diagnosis in our case.

Early diagnosis and treatment of CIDP is necessary to prevent irreversible axonal damage and disability. While multidisciplinary management of CIDP is critical to provide assistive devices, increase strength, and improve quality of life, the mainstay of treatment is pharmacologic intervention. The etiology of this condition serves as the foundation for treatment selection (i.e., IVIG, corticosteroids, and plasma exchange). After discussing the benefits and risks of each therapeutic option, our patient preferred to start with 30 g IVIG infusion therapy. The patient began to run 1 mile daily without lower-extremity weakness or fatigue. For this reason, his sessions were scheduled for every 2 wk, until he was able to run 3 miles daily for 6 d·wk⁻¹. Eventually, IVIG therapy would be scheduled every 3 wk, depending on increased functionality and lack of relapse in between infusion dates. Currently, there are no guidelines regarding long-term management for CIDP (⁶). Doses and duration of treatment depend on when the maximal clinical improvement is reached followed by maintenance management to prevent progression of disease (⁶).

Early diagnosis and treatment were key for clinical improvement and return to baseline athletic performance in this patient. Currently, there are no specific guidelines in a safe return to run program after a CIDP diagnosis. We recommend an individualized return to run program where you start and progress slow following the patient's symptoms and fitness level.

Conclusions

CIDP is a rare, but possible diagnosis in recreational runners presenting to the sports medicine clinic with lower-extremity progressive, painless muscle heaviness and weakness. CIDP is a treatable chronic neuropathy with multiple phenotypic variants that poses a challenge for clinicians worldwide. Clinicians must be aware of the clinical presentation to accurately identify this condition. Clinical history, a complete neurologic examination, electrodiagnostic studies, and a lumbar puncture are essential for diagnosis of CIDP. Treatment with IVIG, corticosteroids, or plasma exchange should be considered for early clinical improvement and fastest return to running.