Adolescent-onset asymmetric muscle wasting and motor-sensory dysfunction with subsequent neurological recovery: A case report

Abstract

BACKGROUND

Progressive focal muscle wasting in adolescents may result from motor neuron, peripheral nerve, spinal cord, or muscular disorders. Atypical distribution and subsequent recovery can complicate diagnosis.

CASE SUMMARY

The patient initially developed pain in the left posterior leg musculature, followed by marked muscle wasting. Involvement subsequently extended to the left upper limb, particularly the biceps, and later progressed more mildly on the right side. At its worst, the illness caused significant functional impairment requiring a walking stick. Marked sensory loss was reported in the affected left limb, with reduced or absent reflexes early in the course. Magnetic resonance imaging of the cervical, thoracic, and lumbar spine revealed no clear structural cause. Following symptomatic management, substantial recovery occurred over the subsequent years, with near normal strength and reflexes and no meaningful functional limitations. However, asymmetric muscle wasting persisted, most prominently in the left calf and upper limb.

CONCLUSION

This case highlights an unusual adolescent-onset neurological syndrome characterized by progressive asymmetric muscle wasting, motor and sensory involvement, severe functional impairment, and substantial recovery with residual atrophy. The atypical distribution and clinical course do not fit neatly into a single classical neurological entity, warranting consideration of an atypical-spectrum presentation of Parsonage Turner syndrome (neuralgic amyotrophy).

Key Words: Adolescent; Muscle atrophy; Parsonage-Turner syndrome; Neuralgic amyotrophy; Multifocal acquired demyelinating sensory and motor neuropathy disease; Case report

Core Tip: Adolescent-onset progressive asymmetric muscle wasting with combined motor and sensory dysfunction can undergo a substantial, functional recovery, even after reaching a severe clinical nadir, although some localized residual muscle atrophy may persist permanently.

INTRODUCTION

Asymmetric, monophasic muscle wasting involving the left upper and lower limbs with sensory involvement is uncommon in adolescents, and the differential diagnosis is broad: Anterior horn cells, peripheral nerves, nerve roots, the spinal cord itself, or skeletal muscle can all be responsible. While considering above mentioned etiological factors of Juvenile-onset multifocal sensory-motor disorders, the list of possible lesions is quite apparent. Anterior horn cells may be affected in poliomyelitis and present as asymmetrical lower motor neuron weakness of lower limb, among adolescents, without sensory involvement[1,2]. Nerve root involvement affects isolated spinal nerve distribution and presents clearly as radiculopathy. Spinal cord disorders present as sensory level, bowel and bladder dysfunction and evidence of cord compression by vertebra or intervertebral disc. A classical example of peripheral neuropathy is Guillain-Barré syndrome. But it is characterized by acute symmetrical bilateral lower and upper limb motor weakness, along with sensory dysfunction due to the post-infectious immunological process. Hirayama disease or monomelic amyotrophy is probably the least likely entity in the above mentioned space. It is juvenile-onset motor disorder that classically wastes and weakens the distal upper limb asymmetrically and essentially motor disorder in nature. Presentations that fall outside this classic pattern, however, are much harder to place[3].

CASE PRESENTATION

Chief complaints

The patient, a 16-year-old male with no relevant family history of neurological or muscular disease, first noticed pain in the left lower limb, concentrated in the posterior leg. What began as pain evolved into neurological dysfunction and progressive loss of muscle bulk, concentrated in the posterior compartment of the left leg. As the illness continued, the left upper limb became involved as well, with the biceps bearing the brunt of it. The right side was eventually affected too, though far more slowly than the left. At the peak of the illness the patient needed a walking stick to get around.

History of present illness

There was nothing in the family history to suggest a hereditary process. There was no personal history of diabetes, hypertension or any medical diseases.

History of past illness

Marked muscle wasting.

Personal and family history

There was nothing in the family history to suggest a hereditary process.

Physical examination

Sensory loss on the left was pronounced. Knee jerk and ankle reflexes were reduced or absent during this early phase. Functions of cranial nerves were normal and examinations of cerebellar functions were also unremarkable. Table 1 shows the difference in the circumference of the calf and upper arm of both the affected and unaffected limbs post recovery. Although evidence-based studies show that depressive illness can commonly happen in this age group, clinical assessment did not reveal any psychiatric illness or drug abuse. It took around 3 years for the patient to recover completely. Figure 1 clearly shows the difference between the calf muscles of both the legs, with marked atrophy in the left leg compared to that of the right. Limb strength was assessed using the Oxford Scale grading system[4]. The findings primarily reflected left-sided involvement, with mild involvement on the right. Table 2 shows the examination performed on the lower limb with characteristic findings post recovery. Table 3 shows the upper limb strength findings initially and post recovery. Note the difference between the upper limb strength and the lower limb strength initially, showing drastic effect in the lower limb compared to the upper limb.

Figure 1 Clinical photographs demonstrating asymmetric muscle wasting of the lower limb after 3 years, with predominant involvement of the left side.

Table 1 Current muscle measurements.

Muscle group	Right	Left
Calf circumference, cm	38	35
Upper arm/biceps circumference, cm	25	24.5

Table 2 Lower limb examination.

Parameter	Strength in left lower leg at initial assessment	Strength in left lower leg post recovery
Hip flexion	3/5	5/5
Knee extension	2/5	5/5
Knee flexion	2/5	5/5
Ankle dorsiflexion	1/5	5/5
Ankle plantarflexion	1/5	5/5
Great toe extension	3/5	5/5
Ankle inversion	3/5	5/5
Ankle eversion	3/5	5/5

Table 3 Upper limb examination.

Parameter	Strength in the left arm at initial assessment	Strength in left arm post recovery
Shoulder abduction	4/5	5/5
Elbow flexion	3/5	5/5
Elbow extension	4/5	5/5
Wrist extension	4/5	5/5

Laboratory examinations

No special notes.

Imaging examinations

Magnetic resonance imaging (MRI) of the cervical, and lumbar spine was obtained but did not reveal a structural lesion that could explain what was happening clinically: Strength testing of both limbs was performed initially and after recovery. No flexion MRI was performed. No major structural abnormality was identified that clearly accounted for the pattern of symptoms. Representative images are shown in Figure 2. Figure 3 shows the MRI images of the lumbar spine. Yet again no major structural abnormalities were identified.

Figure 2 Representative magnetic resonance imaging images of the cervical spine.

Figure 3 Representative magnetic resonance imaging images of lumbar spine.

FINAL DIAGNOSIS

A definitive diagnosis cannot be confirmed based on the existing clinical data and the absence of formal electrophysiological studies. However, the atypical multifocal trajectory, combined motor-sensory involvement, and subsequent recovery allow for several differential possibilities. The primary consideration is an atypical lumbosacral variant of neuralgic amyotrophy (Parsonage-Turner syndrome). A second rare possibility is multifocal acquired demyelinating sensory and motor neuropathy (MADSAM). An acute motor and sensory axonal neuropathy (AMSAN) variant of Guillain-Barré syndrome is considered less likely given the prolonged time course. Finally, classical Hirayama disease is considered the least likely possibility because the clinical distribution—featuring early lower-limb and proximal upper-limb motor and sensory findings—diverges from the pure distal motor upper-limb pattern characteristic of that condition.

TREATMENT

Management was strictly supportive and symptomatic, as no disease-modifying therapy was administered. The pharmacological regimen included: (1) Sinaxamol (orphenadrine citrate + paracetamol, 35 mg + 450 mg tablet), administered twice daily during the acute painful phase for short-term musculoskeletal pain relief; (2) Lacosamide (Nurosa), administered twice daily as a supportive agent for neuropathic pain symptoms during the early progressive phase; (3) Methylcobalamin, administered thrice daily as a neurotropic vitamin supplement; (4) Multivitamins, administered once daily for general nutritional support; and (5) Alprazolam (Nervin), prescribed in low doses for short-term management of situational sleep disturbance and anxiety associated with severe functional impairment, subsequently tapered and discontinued. Patient adherence to medications and physical therapy was reported as good, and no adverse drug reactions or side effects were documented. In addition, structured physiotherapy (consisting of passive and active range-of-motion exercises followed by progressive resistance training) was initiated after the acute phase and maintained throughout the recovery period. All therapeutic interventions were supportive, and the observed recovery represents a natural history rather than a direct pharmacological response.

OUTCOME AND FOLLOW-UP

Roughly three years after onset, the patient was managing daily activities without difficulty; strength and reflexes were reported as normal, and he described no meaningful limitation in mobility or day-to-day function. No fasciculations or tremor were noted at this stage. Despite neurological recovery, residual muscle atrophy persisted, most prominently in the left calf and upper limb.

Longitudinal clinical documentation and timeline

Because this report details a retrospective clinical course, exact calendar dates from the initial presentation years prior were not prospectively captured. Longitudinal documentation was structured using standardized elapsed intervals from symptom onset: Month 0 marked the onset of left posterior lower-leg pain; month 3 represented peak clinical severity (characterized by severe functional impairment requiring a walking stick and medical research council (MRC) strength grades of 1/5 to 3/5); year 1 reflected initial neurological recovery (return of reflexes and substantial functional improvement); and year 3 represented the final clinical follow-up (complete restoration of daily mobility and normal strength, with persistent localized muscle atrophy). Objective clinical tracking relied entirely on validated manual muscle testing using the MRC scale and anthropometric limb circumference measurements, rather than prospective functional scoring scales (Table 4).

Table 4 Clinical timeline.

Time point	Clinical course
Age 16	Onset with left posterior lower-leg pain
Early course	Progressive dysfunction and wasting of posterior left leg muscles
Subsequent period	Left upper-limb involvement, predominantly biceps
Later course	Slow, milder involvement of the right side
Peak severity	Severe functional impairment; walking stick required
Initial evaluation	Reduced/absent reflexes; marked sensory impairment reported
Approximately 1 year	Recovery; reflexes returned almost to normal, with substantial functional recovery
Following years	Gradual, continued functional recovery
Approximately 3 years	Normal daily function, strength, and reflexes; persistent left calf and left arm muscle wasting

DISCUSSION

This unusual longitudinal course began with focal pain in adolescence that evolved into progressive asymmetric wasting and dysfunction, first in the posterior left leg, then in the left upper limb, and later, more slowly, on the right side. This spread pattern points toward a multifocal process rather than a single isolated nerve lesion.

Perhaps the most striking feature is the degree of recovery after such a severe nadir: A patient who once needed a walking stick was, three years later, functioning normally, with strength, reflexes, and mobility restored. Despite neurological recovery, residual muscle atrophy persisted, particularly in the left calf and mild involvement of the left upper limb. Conventional spinal MRI did not identify a structural correlation. Taken together, the clinical trajectory, electrophysiological findings, imaging, and long-term outcome need to be weighed rather than considered in isolation.

The list of possible neurological features has been described in the introduction section. A limitation of this case is the absence of electrophysiological studies, which limited further characterization of the underlying neurological involvement.

Given the lack of formal electrodiagnostic studies, any diagnostic categorization remains speculative. Among potential considerations, an atypical lumbosacral variant of neuralgic amyotrophy (Parsonage-Turner syndrome) is sometimes considered in cases of focal neuropathy[5]. While classical neuralgic amyotrophy typically features an acute, severe neuropathic pain phase followed by patchy multifocal motor and sensory deficits (classically in the brachial plexus, though lumbosacral variants exist), our patient's prolonged, multi-year progressive-then-recovering trajectory deviates from typical presentations, rendering this possibility unconfirmed.

Similarly, MADSAM presents as an asymmetrical chronic inflammatory neuropathy that can mimic multifocal lesions. First described by Lewis and Sumner in 1982, MADSAM is also known as Lewis-Sumner syndrome[6].

Conversely, an AMSAN variant of Guillain-Barré syndrome—while featuring motor and sensory axonal loss—is characterized by an acute-to-subacute monophasic progression reaching nadir within four weeks; thus, the prolonged multi-year progressive course in this patient argues strongly against classic AMSAN, leaving it clinically untenable[7].

Finally, classical Hirayama disease remains unlikely because its hallmark is a pure, non-progressive or late-plateauing motor deficit restricted to the distal upper extremities, entirely lacking the lower-limb onset, prominent sensory loss, and contralateral spread observed here[8].

Taken together, the clinical trajectory, electrophysiology, imaging, and long-term outcome all need to be weighed together rather than in isolation.

CONCLUSION

We describe an unusual case of juvenile-onset progressive asymmetric muscle wasting with combined motor and sensory involvement, a severe functional low point, and substantial though incomplete neurological recovery. Parsonage-Turner syndrome (neuralgic amyotrophy) remains worth considering given the patient’s age and the asymmetry of the wasting, but the distribution here is atypical: The earliest and most prominent findings were in the lower limb and proximal upper limb.